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MALDEN HEALTH SERIES 


PHYSIOLOGY 
AND HEALTH 


y y BY 



M.A., Dr. P. H 


PROFESSOR OF BIOLOGY AND PUBLIC HEALTH, MASSACHUSETTS 
INSTITUTE OF TECHNOLOGY; ASSOCIATE PROFESSOR OF PUBLIC 
HEALTH AND HYGIENE, TUFTS MEDICAL AND DENTAL 
SCHOOLS; DIRECTOR OF HEALTH EDUCATION 
STUDIES AT MALDEN, MASSACHUSETTS; AND 
CHAIRMAN OF THE HEALTH SECTION, 

WORLD FEDERATION OF EDU¬ 
CATION ASSOCIATIONS 



» ■» 


D. C. HEATH AND COMPANY 


BOSTON 

ATLANTA 


NEW YORK CHICAGO 


ATLANTA SAN FRANCISCO DALLAS 

LONDON 











.\ %T 


Copyright, 1929, 

By D. C. Heath and Company 

2 J 9 



PRINTED IN U.S.A. 


NOV 22 1929 

©CIA 14967 


PREFACE 


The student in late junior high school or early senior high 
school is ready for a serious course in the science of physiology. 
This book, therefore, makes a direct approach to this subject. 
Provision is made, however, through the list of health habits 
in the appendix and through the references in the text, to secure 
continuity with the program of health training which the pupil 
has followed in the earlier grades. 

Like the other books in this series, Physiology and Health has 
been developed by the classroom method. On the basis of 
experience thus gained, the discussions of structure have been 
intentionally limited. The illustrations have been carefully 
selected to present anatomical facts and should be regarded as 
study material. Obviously, this course cannot be built upon 
the foundation of biophysics and biochemistry which underlies 
courses in college and professional school. It does seek to 
present in understandable form those fundamental physio¬ 
logical facts which should be a part of the knowledge of every 
well-informed individual. 

I wish to express particular appreciation to Dr. Percy G. 
Stiles, Assistant Professor of Physiology, Harvard University, 
for extensive participation in the preparation of the manuscript. 
Valuable assistance has also been rendered by Miss Georgie 
B. Collins and Miss Adelaide Ross, of the Malden School 
Department, and by Miss Marjory Doherty, Head of the 
Hygiene Department at the Washington Irving Junior High 
School, Boston, in testing and developing the material. 


IV 


PREFACE 


Thanks are also due to Superintendent F. G. Marshall 
and the School Department of the City of Malden for 
continued cooperation. 


C. E. T. 


CONTENTS 


CHAPTER PAGE 

I. The Study of Physiology and Health ... i 

II. Living Cells and Tissues .. . io 

III. Muscles.26 

IV. The Nervous System.43 

V. The Sense Organs .63 

VI. The Health of the Mind and Nervous System 80 

VII. The Mechanics of the Circulation .... 94 

VIII. The Control of the Circulation . . . . 116 

IX. Breathing.126 

X. Food and Digestion.14° 

XI. The Service of the Absorbed Food .... 156 

XII. Particular Foods.164 

XIII. Income and Outgo.173 

XIV. The Teeth.182 

XV. Harmful Substances.199 

XVI. Internal Secretions .219 

XVII. The Body Temperature .228 

XVIII. Muscular Activity .243 

Appendix. 2 62 

Index. 2 8° 



















PHYSIOLOGY AND HEALTH 


I 

THE STUDY OF PHYSIOLOGY AND HEALTH 

What is the most striking difference between animals and ma¬ 
chines? 

Can any machine do the variety of things which the human hand 
can do? 

What is the study of physiology? 

Is there any relationship between health and accomplishment 
in life? 

Today we marvel at the complicated and wonderful ma¬ 
chines produced by man. They do delicate and difficult 
work, but no mechanical device can do as many different 
things as the human hand. It is capable of a strong grasp or 
the most delicate touch. It picks up tiny objects or it lifts 
heavy weights. It adapts itself to various musical instru¬ 
ments. Its movements are quick, strong, graceful. 

Science has given us cameras for still pictures and moving 
pictures. The eye, the camera of the human body, is con¬ 
tinuously transmitting a moving picture during waking hours. 
Automatically it focuses for near and far objects and adjusts 
for bright and dim light. It affords us the beauty of color 
and delicate variations in shade. 

The telephone and radio send sounds over great distances, 
but they are less remarkable than the nerves of the human 
body. The latter send messages which we interpret as sight, 


2 


PHYSIOLOGY AND HEALTH 


color, sound, touch, smell, and pain. Messages come back 
to muscles and glands. These messages travel over the nerve 
paths of our bodies at the rate of 100 yards per second or 
about 200 miles an hour. 



(Reproduced from Ants, by W. M. Wheeler, by courtesy of Columbia University Press.) 


A FUNGUS GARDEN 

This photograph shows the fungus garden in the nest of a species of ant 
which cultivates the plant for food. Here is an interesting example of an 
instinctive action which seems almost intelligent. 

Even in its use of fuel the body is remarkable. What a 
variety of fuel it is able to use! And it uses it economically. 
The food you ate for breakfast is being burned to provide the 
power which keeps your body going through half a day. A 









STUDY OF PHYSIOLOGY AND HEALTH 


3 


small pat or individual serving of butter furnishes enough 
energy to carry a man weighing 154 pounds to the top of 
Bunker Hill Monument, which is 221 feet high. 1 

Most remarkable of all in the animal creations of nature is 
the element of intelligence. The most perfect machine that 
m^n might devise would be lacking in this asset. As we study 
biology, we marvel at the instincts of the birds and insects. 
You know something of the remarkable instinct of birds in¬ 
volved in nest-building and seasonal migration. Bees have 
an elaborate community life with a division of labor among 
different members of the colony. Some ants grow a particu¬ 
lar mold, or fungus, which they use as food. Spiders spin a 
web which helps to capture their prey. Some spiders make 
a loop of the web and go floating through the air clinging to 
this balloon. 

Still more wonderful is the human brain which possesses 
the power to reason. Man appreciates grace, beauty, and 
the arts. 

It has been said that no machines have been developed by 
man for which similar structures or similar activities could 
not be found somewhere in the world of living things. Elec¬ 
tricity existed in the animal world long before man came to 
use it. There are certain fish living in tropical waters which 
have the remarkable power of giving strong electric shocks. 

1 According to Lusk, 1 pound of butter produces energy equivalent to 3440 
calories. A man weighing 70 kilograms (154 lbs.) who climbs 70 meters 
performs work amounting to 4900 kilogrammeters. The mechanical equiva¬ 
lent of heat is 425 kilogrammeters per calorie. The work in this case is actu¬ 
ally equal to about 12 calories, but, since muscle is no more than 20 per cent 
efficient, the expenditure may be set at about 60 calories. This is equivalent 
to the energy produced by 60/3440, or 1/59, of a pound of butter (a little 
more than 54 of an ounce). 


4 


PHYSIOLOGY AND HEALTH 


The currents which they discharge are produced by peculiar 
organs which have been found to be made up of minute units 
which are really electric batteries, placed in orderly rows like 
so many cells in a dry battery. 

How do muscles contract? How are messages sent to the 
brain? Why are bones so strong? How is food changed so 
that it can be carried by the blood? Once you begin to think 
about the marvels of the body, an endless stream of questions 
rises. There is real enjoyment in seeking the answers to 
these questions. 

You have already learned many things concerning the 
care of the body and something of the body itself. Now for 
the first time, however, you have advanced to that point in 
your education where you can begin the careful study of the 
functions of the body, of the way it works. You will find 
few things of greater interest. 

There is a practical side to the study of physiology in addi¬ 
tion to the pleasure of gaining the knowledge itself. A knowl¬ 
edge of the body, its functions, and its care, provides the basis 
for a program of healthful living. Every one develops some 
habits of daily behavior and we would better develop good 
habits than bad ones. The rewards for right habits of living 
are health, vigor, and a feeling of well-being which contribute 
to happiness, efficiency, and success. 

An interesting expression of the relationship between health 
and accomplishment is seen in a statement of the famous ex¬ 
plorer, Richard E. Byrd. He said when discussing the choos¬ 
ing of men for a polar expedition: 2 

“I think that when I consider a man for such an expedition 
as this I put the facing of danger first. I do not mean the 
2 The Saturday Evening Post, April 21, 1928. 


STUDY OF PHYSIOLOGY AND HEALTH 


5 



THE JAVELIN CAST 

This work of R. Tait McKenzie shows the beauty of an athletic body 
and the joy of exercise. 





6 


PHYSIOLOGY AND HEALTH 


sudden emotional courage of a man going over the top, but 
the ability to face protracted danger. . . . 

“Health has much to do with this quality. A man may 
cease to be sanguine after a bad attack of grippe, indigestion, 
or other illness. It is not necessarily a matter of courage at 
all — a man simply may be temperamentally unfitted by mild 
ill health. . . . 

“When a young man stands before me and says yearningly, ’ 
‘I wish you would take me along/ nothing could be more 
helpful at the moment than an exact and confidential chart 
of his past life. I don’t mean anything serious, such as the 
effects of dissipation. They are always visible to the discern¬ 
ing eye. I refer to those small but insidious foxes that tear at 
the vitals of a man without his being conscious of their pres¬ 
ence : overeating, undereating, too many stimulants, too much 
sugar, unbalanced diet, and so on. It makes a magician to know 
just how much harm these little things have done to a man.” 

Let us remember that knowledge alone is not enough to 
produce health. Your health is affected not by what you 
know but by what you do. Only when your knowledge be¬ 
gins to function does it become of health value. You need 
to continue your program of health training, and you will do 
well to consider the rules of health which arise in connection 
with your study of each of the body functions and to check 
your own daily practices against these points. 

It has been said that experience is the best teacher, but that 
the wise man can profit by the experience of others. Experi¬ 
ence is such a costly teacher in health! If you lose your 
health, you may be able to look back upon your experience 
and to tell just how you lost it, but that may not make it pos¬ 
sible for you to regain it. 


STUDY OF PHYSIOLOGY AND HEALTH 


7 


The story is told of an explorer who was seeking the South 
Pole. As he neared his goal, some of his men became ill. 
Should he sacrifice the lives of his men and push on to at¬ 
tain the goal or should he turn back and save the lives of his 
men? He turned back. 

Many persons who fail to take care of their bodies find 
that they have developed a weakness or illness just as they 



SCHOOL SPORTS 

The thrill of a race is one of the rewards for keeping fit. 


are about to reach the goal of their lives. They must choose 
between longer life, at the cost of their objective, or winning 
their objective at the cost of health and perhaps life itself. 

It sometimes happens that young people of high-school age 
feel that they are now old enough and clever enough to drop 
their habits of health along with some of the other habits 
which they followed as children but now follow no longer. 
In youth, health is usually abundant and we are not likely to 
worry about anything of which we have a surplus; but at no 
time is healthful living more important than during the high- 




8 


PHYSIOLOGY AND HEALTH 


school period. Your body is growing rapidly, and your pres¬ 
ent habits will determine in large measure your future health. 

Healthful practices are natural and enjoyable, not irksome. 
We continue them in order that we may maintain a reserve of 
health upon which to draw occasionally in time of need. We 
keep ourselves fit in order that we may have the strength and 
energy to do all the things that we should like to do. 

You have but one body. Each body has its own strengths 
and weaknesses. A study of the mysteries of body structure 
and function is fascinating in itself. In addition, this study 
enables you to plan your program of living in such a way as to 
secure joyous, buoyant, cheerful health. Your program of 
learning and training in health for this year will be one of the 
most interesting school activities you have, if you try to 
make it so. 


Discussion 

1. Make a list of ways in which the human body is superior to a 

machine. 

2. Select the way which you think is most vital and give the 

reasons for your choice. 

3. Discuss the reason Commander Byrd gave for placing health 

as one of the most important qualifications of an Arctic 
explorer. 

4. Name other occupations in which there is a relationship be¬ 

tween health and accomplishment. 

5. Give examples showing that knowledge alone is not enough 

to produce health. 

6. What arguments would you use to convince a boy of high- 

school age that he should continue to practice health 
habits? 

7. Take pencil and paper and in twenty minutes make a list of 


STUDY OF PHYSIOLOGY AND HEALTH 


9 


the things you most want in life. What do you want to 
do, to become, to possess, to achieve, to be? Write these 
down honestly and frankly — not for any one to see, but 
for your own record. When you have finished, take ten 
minutes to look over this list and consider whether health 
will be important in making these things possible. How 
important is it in each case? 


II 


LIVING CELLS AND TISSUES 

What is the unit of structure in the human body? 

How is it possible that the parts of the body can differ so much 
in firmness and strength? 

In a building there are relatively few kinds of materials — 
bricks, wood, iron, glass, for example; is this the case with the 
body? 

How many different kinds of material are in the human body? 

If a boy weighs ninety pounds, what part of this weight is water? 

In studying any mechanism we first learn the units of 
structure and how they are put together. The study of 
biology has shown us that the human body, the lower animals, 
and the plants are all composed of similar structural units. 

Cells. — More than two hundred years ago an Englishman 
who had a chance to use a better microscope than had previ¬ 
ously been available made pictures of what he saw through 
the lenses. One of his drawings was of a thin slice of cork. 
This familiar material is taken from the bark of the cork tree. 
Under the microscope it was found to resemble a honeycomb; 
there were rows and rows of tiny compartments. These have 
since been called the cells of the cork. The bark was dead 
and dry when examined; we know now that if the bark had 
been fresh and living, these compartments would have been 
full of fluid or at least a very soft gelatinlike substance. 
This colorless jelly is the living stuff, or protoplasm. 

Students who have continued to use the microscope through 

IO 


LIVING CELLS AND TISSUES 


ii 



PLANT CELLS 

These are typical plant cells. Note the thick walls and gray pro¬ 
toplasm and the space filled with clear fluid at the center of some cells. 

all these years have found out that leaves and stems of plants 
show a structure which is much like that of cork. They are 
made up of units each one of which is walled off from its 
neighbors, and we still call these units cells. By degrees we 
have become more interested in the parcels of protoplasm 
than in the partitions between them. A wise teacher has said 










12 


PHYSIOLOGY AND HEALTH 



THE AMOEBA 
(Greatly Magnified) 

This is a microscopic free-living single-cell animal which lives in pools 
and streams. 

that it is not the cell but the prisoner in it that we want to 
learn about. 

When the parts of animal bodies came to be studied, it was 
discovered that they, too, are composed chiefly of units which 
we call cells, but these are not separated by noticeable walls. 
The packets of protoplasm are often about the same size as 
the cells of plants. Generally they are pressed close to¬ 
gether, and it seems as if they might run into one mass as 
drops of jelly would be expected to do, yet somehow they re¬ 
main separate. 



LIVING CELLS AND TISSUES 


13 


Free-living cells. — It is not usually possible for any cell 
of the human body to be separated from its neighbors and to 
live long by itself, although by taking the greatest care scien¬ 
tific workers have kept bits of animal tissue living and even 
growing in warm and nourishing liquids. There are, how¬ 
ever, millions of cells which do live apart from others, both 
in the earth and in the water. Since most of these very simple 
forms of life are so small as to be invisible to the naked eye, 
we should know very little about them if it were not for the 
microscope. Some of these free-living cells are green plants; 
some are supposed to be colorless plants; some are spoken of 
as animals. In many cases it is not easy to say which they 
are. Such cells find food of some sort, if they are fortunate 
(enough, and make use of it for their growth. Sooner or later 
each well-grown cell divides to make two. Thus they live 
on as long as conditions favor. Many of them die as the re¬ 
sult of accident, but not of old age. 

The free-living cells that we talk about most often are the 
ones called bacteria . These are very tiny cells which swarm 
in the water and in the surface layers of the soil. The main 
reason why we hear so much about them is that certain kinds 
can live and multiply in the bodies of men and animals and 
cause a number of diseases. Other cells which flourish in 
enormous numbers are those which we call yeasts. While 
these are growing and carrying on their life processes in solu¬ 
tions containing sugar, they produce the changes which we 
know as fermentation. Alcohol is formed by the action of 
yeasts on different kinds of sugar. 

Body cells. — The human body is entirely made up of 
cells or cell products. The skin will serve to illustrate cell 
structure. The cells of the skin are in many layers. Those 
near the surface are dead and dry. They form scales which 


i 4 PHYSIOLOGY AND HEALTH 

are constantly falling off or being washed away. Those which 
lie deeper are alive, and are oval rather than flat in outline. 
You know that if you scrape the skin a little, but not enough 
to make it bleed, you will find moisture. You will also feel 
pain because you are injuring the fine beginnings of sensory 
nerves which are among these deeper cell layers. 



SECTION THROUGH THE CELLS OF THE OUTER SKIN 
(Greatly Magnified) 

Note the thin dead cells at the outside and the thin cell walls. 

The living cells in the skin take in food from the neighbor¬ 
ing fluid, and this enables them to grow, much as the whole 
animal does. But they do not keep growing to an unusual 
size, for now and then each one divides into halves. The 
new cells which are formed in this way are at first smaller than 
the others, but they soon grow to average size. The forming 
of fresh cells makes up for the loss of those which have been 
pushed to the surface and detached. 










LIVING CELLS AND TISSUES 


15 

We ought not to think of the living cells as being hard 
bodies. They are in fact quite yielding. If we could en¬ 
large an average cell a thousand times in each dimension, it 
would probably resemble a raw oyster as much as anything. 
It would be very juicy and easily pressed out of shape. 
Three-quarters of such a cell is water. We shall find that 



DIAGRAM OF TYPICAL CELL 
(After Wilson) 

1. Main body. 2. Nucleus. 3. Attraction sphere. 4. Food par¬ 
ticles and waste. 5. Cell wall. 6. Masses of active material found in 
certain cells, called plastids. 

what gives strength and fixed form to the human body is not 
its cells, but other materials which they deposit about them. 
In spite of the presence of these harder substances — of 
which the mineral part of bone is an example — about two- 
thirds of the weight of the body is due to water. 

When cells are viewed through the microscope, they seem 
at first to have no definite structure. We have said before 
that they appear like tiny drops of jellylike material. But 





i6 


PHYSIOLOGY AND HEALTH 


when these same cells have been carefully prepared for study 
by coloring or staining them with suitable dyes, we find that 
their substance is not the same in every part. Each cell has 
certain parts which can best be understood by referring to the 
picture. The surface is probably different from the interior: 
we say that the cell has a membrane, though we do not mean 
to suggest anything more substantial than a most delicate 
film. Almost always the stain shows a small mass inside the 



STEPS IN CELL DIVISION 
(After Wilson) 

Note that the material of the nucleus divides before the cell body. 

cell which looks as if it were denser than the rest. This is 
called the nucleus. 

When a cell is about to break in two, the nucleus generally 
divides first. At this time it looks as if it contained a snarled 
or knotted thread. The twisted thread breaks up into short 
pieces and these seem to be exactly shared between the two 
new nuclei which are made from the old one. For a little 
while the cell may exist with two nuclei, but soon a crease, or 
groove, runs around it, and this is the beginning of a separa¬ 
tion into two complete cells. 



LIVING CELLS AND TISSUES 


17 


Muscle fibers are really cells. 
These cells are of unusual length, 
but they are the units, the parcels 
of protoplasm, which make up the 
living part of the muscle. Unlike 
the cells of the skin, muscle fibers 
do not divide so as to increase in 
number. When a muscle becomes 
larger as a result of exercise, it is 
supposed that the number of the 
fibers remains just the same as be¬ 
fore, but that the average fiber be¬ 
comes thicker. In the nervous sys¬ 
tem there are peculiar cells of a 
branching form; these do not di¬ 
vide once the brain is fully formed. 
A baby a year old has as many 
cells in his brain as he will ever 
have; his education is carried 
out by adjusting these cells to 
act together, not by adding new 
ones. 

Tissues. — The various kinds of 
material which we find in the body 
are called tissues. Each is com¬ 
posed of groups of similar cells. 
There are four principal sorts, 
two of which, muscular and ner¬ 
vous, have been mentioned. The 
others are the connective and the 
epithelial . 



(Courtesy of D. Appleton & Co.) 

MUSCLE FIBERS 
(Greatly Magnified) 

These cells have been torn 
to show the covering sheath. 
Note : A, The broken end of 
the muscle fibers; B, A bundle 
of fibrils at the torn end; N, 
A nucleus; S, The sheath. 
(From Jordan’s A Textbook of 
Histology.) 










i8 


PHYSIOLOGY AND HEALTH 


Connective tissues, as the name suggests, hold the parts of 
the body together and in shape. Bone is an example. The 
general form of the body depends, of course, on the skeleton. 
Just as the body as a whole has a skeleton, so each organ has 
a framework, though of a more flexible kind. Think, for in¬ 
stance, of a muscle. It could not accomplish anything by its 



A NERVE CELL 
(Greatly Magnified) 

Note the finely branching structure of the cell. 

shortening if its fibers were not bound together and given 
something to pull upon. Tendons unite muscles with bones 
and thus give the muscle fibers a chance to pull upon the 
bones. These white cords, the tendons, are composed of a 
very tough variety of connective tissue. The same tissue in 
the form of thin layers covers the whole muscle on the out¬ 
side and divides it internally into bundles of fibers. You 
have seen these thin white partitions in meat. What we call 
a muscle is really a combination of two kinds of tissue: the 


LIVING CELLS AND TISSUES 


19 

true muscular part which does the work and the connective 
tissue which makes the work effective. 

Other examples of connective tissue are found in the liga¬ 
ments which unite one bone to another at the joints. What 
we call fat is a form of connective tissue in which the cells are 
swollen with oil drops. 

Connective tissues differ from muscular and nervous tis¬ 
sues in that most of the substance of 
connective tissue is apparently quite 
lifeless material. It is not composed 
of cells which are taking food and 
growing, but rather of deposits, or 
cell products. Living cells have made 
these deposits by their own activity, 
but when the tissue has been fully de¬ 
veloped, the cells no longer seem im¬ 
portant. Under the microscope the 
dense, lifeless matter is found to oc¬ 
cupy most of the space. Suppose that 
we are examining a specimen of ten¬ 
don. We find that it is mainly com¬ 
posed of slightly wavy white fibers closely pressed together to 
form bundles. Here and there among these fibers may be 
seen rows or chains of cells. The most remarkable property 
of the tendon is its great strength, and this is not due at all 
to the cells, but to the tough white fibers. Still, it is true that 
the cells made the fibers in the first place, and that if the 
tendon is to be repaired after an injury, these cells have to be 
depended on to provide the new material. 

The structure of bone as revealed by the microscope is very 
interesting. Bone is so hard as to seem almost like a mineral 



CARTILAGE 
(Greatly Magnified) 

Cartilage is a tissue in 
which the cells have been 
separated by the large 
amount of lifeless ma¬ 
terial which they have 
deposited. 


20 


PHYSIOLOGY AND HEALTH 


substance. In fact, a large part of it is a form of lime, some¬ 
what like the material in limestone. This mineral matter re¬ 
mains in its place in a bone which has been in a hot fire, but a 
burned bone is very light and por¬ 
ous. The loss of weight shows 
that originally there must have 
been other substances there. In 
dried bone there are microscopic 
cavities in the hard mass. In life 
each of these cavities is occupied 
by a cell. These cells developed 
the bone by depositing lime salts. 
They continue to live their shel¬ 
tered lives within the bone. Sim¬ 
ilar cells repair injured bone by 
producing a new deposit to cement 
the broken ends together. 

Epithelial tissues serve as cov¬ 
erings, or linings. The outer skin 
is a familiar example. But there 
are other kinds of epithelial tissues 
very different from this. In many 
cases they are composed of cells in 
a single layer, as, for instance, the 
Still more delicate—.suggesting 
films of bubbles — are the partitions between the air and 
the blood in the lungs. 

It might seem that epithelial tissues, like connective tissues, 
have little or no action of their own. A mere covering or lin¬ 
ing for a part of the body need not necessarily be alive. Yet 
most of the epithelial cells are probably living. This makes 



CROSS SECTION OF BONE 
SHOWING MINUTE 
STRUCTURE 
(Greatly Magnified) 

i. Surface layer of bone. 
2. Deeper portion. 3. Canals. 
4. Location of cell. 

lining of the intestine. 





living cells and tissues 


21 


it possible not only for new ones to take the place of old, but 
also for other activities to go on. Epithelial cells have at least 
two forms of activity which we must not neglect to mention: 
they have to do with absorption and with secretion. 

These two processes seem to be opposites, yet in some re¬ 
spects they are very much alike. Absorption is the taking in, 
through layers of cells, of substances dissolved in fluids; 
secretion is the passing out, through layers of cells, of other 
dissolved materials. The food we have 
eaten and digested has to be absorbed 
through the epithelium of the intestine. 

Secretion is illustrated by the working of 
the concealed organs (glands) such as 
those which produce the tears and the epithelial cells 
saliva. To absorb or to secrete, the cells or THE CHEEK 

must be truly alive. _ (Greatly Magnified) 

Perhaps we should explain what is 
meant by a gland. You have seen drops of perspiration ris¬ 
ing from the pores of your skin. Each of these pores is the 
opening of a tiny tube made of epithelial cells. The tube is 
much coiled and closed at the deep end. It is wrapped around 
with a network of fine blood vessels. The coiled tube is a 
sweat gland; its cells receive water and some dissolved ma¬ 
terial from the blood, and they discharge this fluid through 
the slender outlet which leads up to the pore. In the lining 
of the stomach there are glands opening to the surface in 
much the same way. They secrete the gastric juice. 

The glands we have just mentioned are very small. The 
body also contains large glands, like the liver. This is a mass 
of seemingly solid tissue weighing as much as three pounds. 
When thin sections of it are examined with the microscope, 



Nucleus 


22 


PHYSIOLOGY AND HEALTH 


the whole substance is seen to be made up of secreting tubes 
of epithelium, closely packed together. In this case the 
neighboring tubes unite to form larger ones, and these join in 
turn until finally the secretion, or bile, is all conducted out of 
the liver by a single passage. The outlet of such a compound 
gland is called a duct. The main duct with its branches ex- 



(Greatly Magnified) 

The ducts through which the secretion escapes are marked with “+”. 

tends to all parts of the organ as the roots of a plant might 
reach to all parts of a pot filled with earth. Ducts from the 
salivary glands send saliva into the mouth through small 
openings in the cheeks and under the tongue. 

The work of cells. — When a single cell has to get along 
by itself, it must do many things; it takes in food, throws off 
waste, breathes, and reproduces itself by the process of divi¬ 
sion. Many of these single cells can move about, and they 








LIVING CELLS AND TISSUES 


2 3 


all respond in some way when things happen to them. When 
many cells are in a close partnership, as is the case in our own 
bodies, matters are somewhat different. Here we have what 
is called ‘a division of labor.’ Certain cells do particular 
things most of the time and rely on their neighbors for help 
to make this possible. For instance, the cells of muscles 
have the power to contract, but they depend on the coopera¬ 
tion of other tissues to get the food they need, and to attend to 
the supplying of their oxygen and the removal of their 
wastes. The cells of the nervous system have a wonderful 
service to perform, but they have to be fed and sheltered and 
transported from place to place in the world by cells located 
in other tissues. 

You will see that the body is like a civilized community, or 
society, of which the cells are members. When it is found 
that a man has a very remarkable talent — perhaps as a 
musician, a ball player, or physician — people usually co¬ 
operate to help him to do his best in his own line. They re¬ 
lieve him of all other work. They feel fully repaid for all 
that they do for him because of the pleasure or service he 
gives them in return. The tissues of the body behave in 
much the same way. We do not mean that the individual 
cells feel responsibility or gratitude, but they act much like 
the citizens in the cases we mentioned. Vast numbers of 
muscle and gland cells seem to be at the service of the nervous 
system, but it is not a one-sided relation, for their own wel¬ 
fare depends on the performances of the brain. 

A man may be cast away, like Robinson Crusoe, yet man¬ 
age to keep himself alive. He can find food and cook it; can 
shelter and clothe himself. But all of these needs would be 
better attended to if he could have the cooperation of other 


24 


PHYSIOLOGY AND HEALTH 


men and women with special training. You can see that 
highly civilized people are safer and happier when they are 
living in large groups. Savages, on the other hand, may be 
better off when they are scattered, because they are all after 
the same things and are not of much help to one another. 
That is the way with single-cell animals. In the bodies of 
the higher animals there is much variety in the types of cells 
and in their work. So, too, there is increased dependence 
of each part upon all the rest. 

Substances in the body. — We have described the living 
structures of the body without attempting to tell of what ma¬ 
terials they are made. The protoplasm of living cells is com¬ 
plex, and a wide knowledge of chemistry would be necessary 
to begin to understand its exact nature. You are already 
familiar with some of the substances of the body, such as fat, 
iron, sugar, lime, sulphur, and water. Your later study of 
science will give you a knowledge of many other interesting 
substances which are to be found in the human body. 

Discussion 

1. What is the usual meaning of the word ‘cell’? How has 

the meaning changed since the word was first used? 

2. What do you understand by protoplasm? 

3. What do cells need? 

4. What are tissues and what are the chief kinds? 

5. What is meant by the division of labor among cells? Illus¬ 

trate. 

6. Discuss the nature and the importance of the substances 
produced by cells in the connective tissues. 

Contrast the life processes of free-living cells with those of 
cells in the human body. 


7. 


LIVING CELLS AND TISSUES 


25 

8. What have you learned in this chapter which would suggest 
the importance of drinking enough water? 

Experiments 

1. Burn a piece of bone where there is a good draft. Bring it 

to class. Note its lightness and the small cavities all 
through it. Explain this condition. 

2. Let some one go to the butcher shop or market and get a piece 

of tendon to bring to the class. Does it stretch? Can 
you pull it in two? Does it cut easily? 

3. If you have a microscope at school, perhaps your teacher 

will help you to see some living cells through it. Yeast 
cells may be seen by soaking a yeast cake in water and 
putting a drop of the water on a glass slide for study under 
the microscope. Green plant cells may be secured by 
scraping off the green growth sometimes seen on the bark 
of trees and putting these single-cell green plants ( Pleuro- 
coccus) under the microscope on a glass slide. 


Ill 


MUSCLES 

Can you tell just what happens when you lift your hand? 

What is the source of power to move the human body? 

Have you ever seen muscle tissue? Where? 

Do muscles produce every movement of the body? 

What substances are used by muscles? 

Does muscle produce waste products? 

Every boy knows that his muscles are the motors, or en¬ 
gines, which set the parts of his body in motion. He feels 
them tighten and grow hard under the skin and understands 
that somehow certain muscles move his arms and legs. 
Other muscles change the expression of his face; still others 
keep his chest rising and falling as he breathes. 

The muscles make up about half the weight of the body. 
In the newborn baby they probably do not make up so large a 
part; as a child grows from year to year the gain in muscle 
goes on faster than the gain in some other kinds of material. 
The muscles are the only parts of the body which have power 
to move; the other parts must be carried or moved by them. 
The muscles of certain animals are familiar to us as meat. 
To be sure, some portions of the body which are not muscle 
are eaten as meat — the liver, for instance, or tripe, which is 
the lining of the stomach — but steaks, chops, and roasts are 
cut from the large muscles which were used to move the legs 
or ribs of the steer or the sheep when the animal was alive. 

26 


Phalanges 


MUSCLES 


27 



THE HUMAN SKELETON 















Serratus 


PHYSIOLOGY AND HEALTH 



Rectus 

Femoris 


Tibialis 

Anticus 


of the Toes 


Sterno-mastoid 


toralis Major 


Sartorius 


Vastus Externus 


tensors of Fingers 
Flexors of Fingers 


Triceps 

Biceps 


FRONT VIEW OF IMPORTANT MUSCLES 









MUSCLES 



Latissimus Dorsi 


Gluteous Maximus 


Vastus Externus 


Flexors of Toes 


Biceps Cruris 


G astrocnemius 


Tendon Achilles 


Triceps - 


Flexors 
of the 
Hand 


Extensors of the 
Hand 


Deltoid 


2 9 


BACK VIEW OF IMPORTANT MUSCLES 












30 


PHYSIOLOGY AND HEALTH 


Nature of muscle. — A muscle may be of almost any shape 
or size. Suppose we think of the one on the front of the arm 
between the shoulder and the elbow, which a boy is often 
proud to show to his friends. This is called the biceps. It is 
thickest in the middle and narrows toward the ends. If we 
could see it, we should find its thick middle part reddish in 
color. Near the ends it becomes slender and very firm and 



ACTION OF OPPOSING MUSCLES 

This diagram illustrates the opposed relation of the biceps and triceps 
muscles. 

tough. These slender white ends are the tendons of the 
muscle, and they are attached to the bones. The thick red 
part of the biceps contracts and makes the movements. 

The tendons apply the force to the bones. They are like 
the traces which make it possible for a horse to pull a wagon. 
We must remember that muscles do all their work by pulling; 
they never push. When the biceps shortens and thickens, it 
raises the forearm and hand as the elbow is bent. The biceps 





MUSCLES 


31 



THE PRINCIPLE OE OPPOSING MUSCLES 

The cords which turn a rudder illustrate the principle of opposing 
muscles. 

muscle swings the forearm up in much the same way that a 
boy raises a fish pole. A study of the diagram will show the 
similarity of the movements. We can make such movements 
slowly or quickly, with little force or much, as we choose. 

The different muscles of the body are usually so arranged 
that if one of them can move a part in a certain direction, 
there will be another of them fitted to make the opposite 
movement. Think again of the biceps raising the forearm 










3 2 PHYSIOLOGY AND HEALTH 

or the fish pole. If the muscle should stop pulling and grow 
limp and soft, the arm would drop back. The weight would 
make this happen; but there is a muscle on the back of the 
upper arm which can give extra force to the downward move¬ 
ment. This muscle is called the triceps. It is used in 
straightening the arms, as in striking a 
blow wfith a hammer. You can see that 
when the biceps shortens, the triceps 
must be stretched, while the triceps in 
turn can pull against the biceps and 
stretch it. These two muscles act, one 
against the other, in the same way as 
do the two lines which turn the rudder 
of a boat. One line swings the rudder 
to the one side, the other to the opposite 
side. 

All over the body the muscles are 
arranged in this way, one balancing an¬ 
other. There are muscles which pull 
down the lower jaw and open the mouth, 
while very much stronger muscles raise 
the jaw in biting. These latter muscles 
are so strong that the pressure between 
the back teeth when one is biting hard may be as much as two 
or three hundred pounds. There are muscles which bend the 
body forward and others which straighten it; these two sets 
work by turns when a man is rowing. 

Muscle fibers. —Every muscle is made up of an immense 
number of tiny parts which we call fibers. These are about 
as large as hairs, and they are packed in bundles side by side. 
Each fiber is really a little muscle which can shorten and pull 



VOLUNTARY OR 
STRIPED MUSCLE 


Notice the relation 
between the fine blood 
vessels and the muscle 
fibers. (See also the il¬ 
lustration on page 33.) 













MUSCLES . 


33 


to do its share in the work of the whole. Muscle fibers are 
often about an inch in length. Remember that lean meat is 
muscle. When we look at well-cooked pot roast or corned 
beef, we see how it falls apart in little strips. We say that it 
has a ‘grain.’ The fibers of the muscle run lengthwise of 
the grain, and when living muscle shortens, it does so in this 
direction. 

What makes muscles contract. — The muscles that we 
have been talking about are often called voluntary. This is 
to express the idea that they usually 
do what we wil 1 them to do. The brain 
is the organ which we use when we 
think, and there are connections be¬ 
tween the brain and the muscles. 

These connections are made by means 
of fine threads which we call nerve 
fibers. A muscle like the biceps has a 
great many of these fibers leading into 
it. They come to it from a great 
bundle of such fibers called the spinal 
cord, which extends down the back 
from the brain itself. 

Voluntary muscles never work of themselves; they are al¬ 
ways called into action through their nerve fibers. If the 
fibers which go into a certain muscle have been accidentally 
cut or destroyed by disease, we say that the muscle is para¬ 
lyzed. This expression means that the owner cannot make 
it work at will. It remains idle and after a time wastes away. 

In all parts of the body nerve fibers are found collected into 
shining white bundles which we call the nerves. Any nerve 
large enough to be seen without a microscope consists of a 



STRIATED MUSCLE 


Note the attachment 
of the nerve fibers to the 
muscle fibers. 



34 


PHYSIOLOGY AND HEALTH 


great many fibers. They are bound up in the nerve much 
as telephone wires are wrapped up in cables. 

Nerves have no power of movement. What passes along 
the nerve fibers from the spinal cord to the muscles reminds 
us of the electric current used in telegraphing or telephoning, 




Cable (n&tuv&l size) 

A NERVE AND A TELEPHONE CABLE COMPARED 
This diagram shows the similarity in structure between a nerve and a 
telephone cable. The actual size of the nerve is that of the finest thread. 

though it is not exactly the same. We may say that nerve 
fibers make it possible to send signals to the muscles. When 
the signals are received, the muscle fibers are put to work. 
Every muscle fiber is supplied with a nerve fiber which comes 
from the spinal cord, and which, through other fibers in the 




MUSCLES 


35 


spinal cord, connects the muscle fiber with the brain. Many 
nerve fibers branch in such a way as to reach several muscle 
fibers. 

What furnishes the power to muscles. — A muscle is in 
some ways like an engine. It does work and gives out heat. 
The heat and work which we notice with an engine are pro¬ 
duced by burning some kind of fuel, usually coal or gasoline. 
Similarly, a muscle cannot go on working unless it is supplied 
with the right sort of fuel. Coal, firewood, and gasoline have 



THE RELATION BETWEEN NERVE CELL AND MUSCLE 

This diagram shows how several muscle fibers may be governed by one 
nerve cell. 

a store of power, or energy, locked up in them which is set 
free when they are burned. The motor car has to go to the 
filling station, and the railway engine to the coal shed. We 
might say that each has to be fed. A great part of our 
food, after its digestion, is given to the muscles and used up 
by them in order that the energy which is hidden in the food 
may be turned into movement. We may say that such food 
is ‘ burned’ by the muscles. Of course, they do not produce 
flame and smoke, but the food is really destroyed in nearly the 
same way as though it were thrown into a fire. A great deal 













PHYSIOLOGY AND HEALTH 


36 

of heat results. You have noticed how you are warmed by 
exercise. At this time the muscles are burning fuel rapidly. 

The steam engine needs air as well as fuel. The gasoline 
which is exploded in the cylinders of the automobile must first 
be mixed with air. Air is a mixture of gases. A particular 
gas called oxygen, which makes up about one-fifth of ordinary 
air, is needed for the burning of fuel. Oxygen is always used 
when the forces locked up in coal, gasoline, or food are made 
to do work. 

Muscles need to have a supply of oxygen, and the harder 
they work, the more rapidly this oxygen must be brought to 
them. The air which we breathe gives oxygen to the blood 
in the lungs, and the blood carries it to the muscles. Here 
the blood shares its oxygen with the muscle fibers. 

Waste materials from muscle action. — As the muscles 
work, they not only use oxygen but they also have to be re¬ 
lieved of waste materials. We have seen that the blood com¬ 
ing into active muscles brings them oxygen. As the blood 
stream flows on, it carries away the wastes which have just 
been formed. The tubes which bring the blood into muscles 
are the arteries, and those which take it away are the 
veins. 

It happens that the chief waste produced by the activity of 
muscles is actually the same as that which is formed when 
coal is burned. This is carbon dioxide gas. This gas goes in 
great quantities up the smokestack of the steamer, and we 
ourselves have to get rid of it in large amounts, especially 
when we take exercise. We are always producing some car¬ 
bon dioxide, for our muscles are never completely idle. Some 
of the muscles are always in use to carry on breathing, and 
unless we are lying down, others have to be active in order to 
keep the body from falling in a heap. When a boy is hard 


MUSCLES 


37 



at work, running perhaps, he may use ten times as much oxy¬ 
gen as when he is resting. At such a time he will also pro¬ 
duce ten times as much 
carbon dioxide as he does 
when he is quiet. 

How does the carbon 
dioxide find its way from 
the muscles to the lungs? 

This waste substance is a 
gas, the same one which 
forms the bubbles in soda 
water. The blood washes 
carbon dioxide from active 
muscles and carries it 
away. When such blood 
is in the veins, the gas 
which it bears is not in the 
form of bubbles, which 
could be seen, but is said to 
be dissolved. You know 
that you cannot see the gas 
in ginger ale until the bot¬ 
tle is uncorked. In the 
lungs the waste gas leaves 
the blood and is breathed 
out with the air. 

Fatigue. — If you have 
the idea that muscles do 
their work much as en¬ 
gines do and really depend 
on fuel and oxygen to give them power, you can understand 
something about what happens when we grow tired. At least 


THE MARATHON RUNNER 

The fatigue of the Marathon runner 
conies in large measure from his hav¬ 
ing used up most of his fuel supply. 





PHYSIOLOGY AND HEALTH 


38 

three things may stop the working of an engine. First, the 
fuel supply may give out. Second, something may block the 
stream of fresh air which has been entering the furnace. 
Third, a waste substance produced in the burning of the fuel 
may clog the moving parts, just as carbon sometimes gathers 
in the cylinders of an automobile engine and interferes with 



FINISH OF A HUNDRED-YARD DASH 

The athlete who runs a short distance at top speed suffers from want 
of oxygen. 


its operation. The ways in which living muscles may be 
hindered in their activity are much like these. 

The condition of a man who is finishing a Marathon race 
will illustrate shortage of fuel. That is not the whole story, 
but it is an important part of it. This athlete has run more 
than twenty-five miles. He has not traveled fast enough to 
be in great want of oxygen; his lungs and circulating blood 





MUSCLES 


39 


are still bringing plenty of this gas to his muscles. However, 
the blood itself is not so well supplied with fuel of the right 
sort as it was at the start. 

At another time an athlete may put out all his power in a 
minute or even less. This may be the case when he runs a 
quarter of a mile at his best speed. His fatigue comes mainly 
from lack of oxygen. His muscles have demanded more of 
it than the blood could give them, so that his fuel is not 
properly burned. Waste products are not removed rapidly 
enough and interfere with the working of his muscles. We 
say that he is ‘all in,’ but this condition is only temporary. It 
will not take him long to recover completely and be able to re¬ 
peat the run. For a time he has to breathe hard, so that extra 
amounts of oxygen shall be carried to his muscles until their 
condition is normal once more. 

From what has been said you can understand that a boy 
may be tired and obliged to give up working either because 
his fuel is becoming scarce or because oxygen is not given to 
the muscles in the full amount which they are demanding. 
Probably there are still other changes in the muscles when 
they are fatigued. Some of these changes may be more or 
less like the clogging of moving parts which has been men¬ 
tioned. A tired muscle feels lame and stiff. This feeling 
is a sign that there has been a change of condition of some 
sort. It shows us that there are nerve fibers which carry 
messages to the spinal cord from the muscles. Perhaps there 
has been a kind of poisoning because waste substances have 
been formed more rapidly than they could be removed by the 
blood. Perhaps there has actually been some slight tearing 
of the fibers or the other material in the muscle. The un¬ 
comfortable feeling is really of use to us; we know that our 


40 


PHYSIOLOGY AND HEALTH 


muscles are not at their best and usually we are thus kept 
from forcing them to work when harm might be done. 

Other kinds of muscle. — When we speak of muscles, we 
almost always mean those organs which cause the visible 
movements of the body, acting under the direction of the 
nervous system and pulling upon the bones. We have been 
talking entirely of these muscles *so far. They are often 
called skeletal because they have such an important relation 
to the bones of the skeleton. They are also called voluntary 
because of their employment in making intentional move¬ 
ments. 

There are two other kinds of muscle, or contractile tissue. 
One is the remarkable variety which is found in the heart and 
is responsible for its beating. This kind is called cardiac 
muscle. It does not require a connection with the nervous 
system in order that it shall work; it is said to be automatic, 
for the power to move, to keep the heart beating, is within 
itself. 

Another kind of muscle is found in many of the internal 
organs. It is called by various names such as plain, smooth, 
or involuntary . When the cells of such muscle change their 
length, they do so rather gradually; they never jerk or twitch. 
Smooth muscle is found in the wall of the stomach and the 
intestine. It usually exists in thin sheets. When these 
sheets contract or relax, they change the size of the enclosed 
cavities. Smooth muscle cells are present in the walls of 
blood vessels and serve to change the diameter of these pas¬ 
sages. This is a very important service, as we shall see. One 
of the most remarkable properties of this kind of muscle is its 
ability to hold a certain degree of contraction for a long time 
without seeming to become fatigued. It is to some extent 


MUSCLES 


4i 


automatic. Small specimens removed from the stomach may 
show a slow beating, though the tendency is not so marked 
as with the heart. 


Discussion 


1. Describe the biceps. 

2. Describe a tendon. Where are tendons found? What 

work do they do? 

3. Explain the action of the biceps and triceps when we take 

the command, “Arms upward bend! Position!” or in 
using a fishing rod. 

4. Name a voluntary muscle. Explain how it contracts. 

5. How do the muscles get energy for their work? 

6. What is the chief waste product of muscle activity? Why 

does it vary in amount? How do we get rid of it? 

7. Is there a difference in what happens to the body when one 

is tired from a short, fast run and when one is tired from 
a long, slow run? 

8. Look up in the appendix the health habits related to exer¬ 

cise and discuss them in the light of this chapter. 

9. What opposite movements can you name which show the 

action of balanced or opposing muscles? 

10. Is there a difference in the size of the arm and shoulder 
muscles of different boys? Why? 

Experiments 

1. Have some one bring a small piece of boiled meat or cooked 
corned beef to school, or look at the slice of meat in a 
corned-beef or ham sandwich. Note the grain of the meat. 
Can you separate it into fine shreds?- When the muscle 
was alive, in which direction did it contract? Do you see 
any evidence of what was formerly connective tissue 


42 PHYSIOLOGY AND HEALTH 

which, in the process of cooking, has been turned to jelly? 
When these tissues were alive, the muscle was the softer 
and the connective tissue the tougher. Is that still the 
case? How does cooking make meat more tender? 

2. Burn a small quantity of fat and an equal quantity of sugar. 

Which gives off the more heat (energy) ? 

3. Contract the biceps muscle of the left arm. Contract the 

triceps muscle. Notice the difference in the hardness of 
each muscle in the contracted and relaxed condition. 

4. Demonstrate the action of a boy fishing and explain the move¬ 

ments of the muscles. Do the same with the movements 
of rowing. 

5. Make a cardboard model of an arm with a joint at the elbow. 

Use strings to demonstrate the pull of the biceps and of the 
triceps. 

6. Watch the movements of the eye when a person is reading or 

looking out the window of a moving car. Note the speed 
with which the eye moves. 

7. See how many pencil dots you can make on a sheet of paper 

in fifteen seconds. How many muscle movements (two 
for each dot) were made per second? 


IV 


THE NERVOUS SYSTEM 

What are nerves? What do they do? 

How does the nervous system control breathing without any 
thought on your part? 

How long does it take to shut the eye if something unexpected 
is coming toward it? What causes the eye to close? 

Are the brains of two month-old babies more similar than the 
brains of two five-year-old children? What has made the 
difference? 

What do you remember most clearly about your early childhood? 

Do different members of the class have the same memories? 

Which side of the brain is used when we move the right arm? 

The work of nerves. — You know that the muscles of the 
body are made to work at the right times because they receive 
what we have called ‘signals’ from the brain. Each muscle 
fiber, you remember, has a slender nerve fiber joined to it. 

When a charge of gunpowder has been placed in a hole 
drilled in a ledge, the blast is often fired by means of electric 
wires. These may be very long. The contraction of muscle 
fibers is in many ways like an explosion, and the nerve fibers 
bring about this contraction somewhat as the electric wires 
bring about the explosion of the blasting powder. Of course, 
this comparison is not exact in every respect, but it is a help. 
When the blast goes off, there is movement and heat, but the 
wire that was necessary to the result did its part without mov- 


43 


44 


PHYSIOLOGY AND HEALTH 


ing. So the nerve fibers call the muscle fibers into action 
without having themselves any power to move. 

Something similar to an ordinary electric current flashes 
along the fibers. These fibers make up the greater part of 
the nervous system. This signal, as we have called it, 
travels at a high speed — faster than a railroad train; prob¬ 
ably as fast as an aeroplane doing its best. You can see that 
it does not take more than a small fraction of a second for 
this signal to cover the longest dis¬ 
tance in the human body. If our 
actions are delayed, then, the fault 
is not with the nerve fibers. 

These conductors have still an¬ 
other property which reminds us of 
electric wires. They seem to do 
their work with very little wear 
and tear. Muscles spend fuel and 
become fatigued when they are ex¬ 
ercised. We cannot say that 
nerve fibers serve us without using 
up some kind of fuel, but we are 
certain they use but little of it. 

Nerve fibers are used for other purposes besides calling 
muscles into action. Sometimes they cause the organs which 
we call glands to get busy making new materials. Suppose 
a boy gets a cinder in his eye. He blinks, and this shows 
that the nervous system is stirring up certain muscles. But 
at the same time his eyes fill with tears. This is because the 
small organs which are capable of manufacturing the tears 
have been set to work through the influence of the nerve 
fibers leading to them. Saliva flows when food is taken into 



TWO VERTEBRAE AND A 
PORTION OE THE 
SPINAL CORD 

This shows how the spinal 
cord passes through the 
spinal canal and how the ver¬ 
tebrae rest on cartilage. 




THE NERVOUS SYSTEM 


45 



DIAGRAM OF THE NERVOUS SYSTEM 


PHYSIOLOGY AND HEALTH 


46 

the mouth or even at the sight or smell of food when we are 
hungry. This is another illustration of the control of glands 
by way of the nerve paths. The production of tears or saliva 
in such cases is called secretion. 

Besides the nerve fibers which influence muscles and glands 
there are those which carry their signals in the opposite direc¬ 
tion — from outside the spinal cord and brain into those 
regions. These are usually called sensory fibers. In the 
head, where the eye, the ear, and the organs for smelling 
and for tasting are located, the sensory fibers are in a great 
majority. All that we learn about the world around us we 
owe to these pathways. At another time we shall say 
more about the eye, the ear, and the other organs of the 
senses. 

You know that the brain fills the main cavity of the skull. 
Descending from the brain through a large opening in the 
base of the skull is the spinal cord. This is about the size 
of one’s little finger and perhaps 20 inches long. It is en¬ 
closed by the arches of the small bones (vertebrae) which are 
stacked to form the spinal column. The nerve fibers which we 
have been talking about are gathered into bundles called 
spinal nerves and these unite with the spinal cord, reaching 
it through notches between the vertebrae. There are thirty- 
one pairs of such nerves, each containing thousands of fibers. 
The majority of these fibers are of the sensory kind. The 
diagram shows that each spinal nerve when close to the cord is 
split into two divisions, or roots, and it is an interesting fact 
that the sensory fibers sweep around to enter the back side 
of the cord, while the motor fibers are in the roots which 
spring from the front surface. The fibers of the spinal 
nerves reach all parts of the body excepting the head, which 


THE NERVOUS SYSTEM 


47 

is supplied by cranial nerves leading to and from the brain 
through small holes in the skull. 

Now we may show how the fibers that conduct inward and 
those that conduct outward are arranged to work together. 
This is the basis of what is called reflex action. 

We were speaking just now about the boy with a cinder in 
his eye. We know that this boy feels discomfort or pain. 
He could not have this experience unless there were sensory 
nerve fibers leading from his eye to his brain. The pressure 



CROSS SECTION THROUGH THE SPINAL CORD 
(Greatly Magnified) 

This shows the origin of a pair of nerves and the path of a nerve impulse 
in a simple reflex. 

and rubbing of the cinder against the beginnings of the nerve 
fibers near the surface of the eyeball and in the lining of the 
lids cause them to send pain* messages inward. A disturb¬ 
ance of some kind occurs in the brain. The pathways leading 
in are in some way related to others leading out. The wink¬ 
ing and the flow of tears which we mentioned are the result of 
this combination. 

Reflexes. — When something happens to a part of the body 
and there is conduction from that part to the central nervous 
system, there may be a feeling or there may be a reflex act or 






PHYSIOLOGY AND HEALTH 


48 

both. The reflex is a movement or a secretion or some other 
sign of change in response to the condition which came first. 
It does not depend on feeling or will. Most reflexes are use¬ 
ful. For example, in the case already mentioned the blinking 
and the rush of tears help to get rid of the cinder. 

Similarly, if a bit of food goes the wrong way — that is, 
gets a little distance down the air passages, where the lining 
is well provided with sensory fibers — there is reflex coughing. 
The nerve paths leading from the throat to the brain are so 
connected with the nerve paths returning from the brain to 
various muscles that the cough is bound to come. It will 
usually remove the bit of food. 

Sneezing when anything tickles the inside of the nostril is 
another reflex act. It is a good illustration, because sneezing 
is something which we cannot do on purpose. We can 
wink and cough when we choose, but we have to wait for some 
special condition to make us sneeze. 

If a child touches a hot stove, he quickly draws his hand 
away from it. If he is asked to tell why he did this, he will 
probably say that he was hurt and then pulled his finger away. 
But the movement at such a time is actually quicker than the 
feeling. The finger is snatched away and the pain is realized 
an instant afterward. We are better protected from dangers 
of many kinds than we could be if each injury had to make 
itself felt before we could do something to escape it. Another 
point is that we do not have to give our attention to this class 
of movements. While we wink or cough or sneeze, we can go 
on thinking of other things. 

Another good example of a reflex act is the knee jerk. If 
you strike a sharp blow just below the kneecap when the foot 
is swinging free, there will be a quick contraction of the 


THE NERVOUS SYSTEM 


49 


muscles on the front of the thigh and the foot will be swung 
forward. The blow acts through the skin on the tendon be¬ 
neath and the signals run from the knee to a central station 
causing other signals to flash down to the muscles. The knee 
jerk is a very prompt and simple reflex. Physicians pay 
much attention to it because in some diseases of the nervous 
system it is lost, while in others it becomes stronger than 
normal. 

Not all reflexes are so simple and easily understood as those 
that we have been using as illustrations. Take the matter of 
keeping one’s balance. We are able to do this for the most 
part because whenever we sway more than a very little for¬ 
ward or backward, to the right or the left, the signals are 
quickly sent for a muscular act to reverse the motion. 

When we talk about our reflexes, we are apt to have in 
mind the effects produced by objects coming in contact with 
the body. There are other reflexes in which the changes that 
start the process are internal. When we inhale (breathe in), 
we stretch the elastic lungs. As soon as this stretching reaches 
a moderate degree, certain sensory fibers signal to the brain 
and the muscles promptly alter their action so that the chest 
begins to fall and we find ourselves exhaling (breathing out). 
We do not have to think about the shift. It would be strange 
if we had to attend to it sixteen times every minute. 

Most of the familiar examples of reflex action are found in 
sudden adjustments to meet changes in our surroundings. On 
the other hand, reflexes may be gentle and gradual. Sup¬ 
pose that the skin is warmed and becomes flushed. The 
warmth has affected certain sensory nerve fibers in the skin. 
They have sent their message to the spinal cord. Another 
message has returned from it to the blood vessels of the skin 


5o 


PHYSIOLOGY AND HEALTH 


and has relaxed them, allowing more blood to flow near the 
surface. Thus the flush becomes noticeable. If the warm¬ 
ing has been of greater amount, sweat appears, rising in drops 
from the pores. This is a reflex secretion like that of tears or 
saliva. 

We ought to think of the brain and the spinal cord as the 
places where the nerve messages from the sense organs are 
received and sent on to direct the use of muscles and glands. 
You may be reminded of a telephone exchange. A subscriber 
calls up ‘Central.’ He gets his connection with the house he 
asks for. While he has this connection, he is able to give di¬ 
rections to the man at the receiving end of the line and so set 
him to do a piece of work. The operator may be interested 
in this affair or she may not. In much the same way we our¬ 
selves, as persons, may take some notice of the reflex actions 
which are going on, but usually they pass unnoticed. Be¬ 
cause this is possible we are relieved of a great burden. So 
many of the changes that are made by various parts of our 
bodies are quite unconscious that we are given freedom to at¬ 
tend to other things which are new and interesting. 

The longer the list of reflexes that we make, the more we 
come to see how these actions help to save the body from 
being injured in various ways. Now and then we cannot 
make out that a reflex has any such value. When a man goes 
to sea for the first time the rise and fall of the ship is likely to 
make him seasick. The reflex symptoms are not to his 
advantage. In cases of this kind we shall probably find that 
the parts of the nervous system responsible are being severely 
overworked or affected in unusual ways. 

Habits. — There is a close relationship between reflexes 
and habits. We say that a baby has reflexes and that an 


THE NERVOUS SYSTEM 


51 



REFLEX ACTION 

This diagram shows how the nervous system causes the finger to be 
withdrawn — a protective reflex. 


older child forms habits. The baby promptly sucks the 
nipple of a bottle when it is brought to its mouth; this is a 
reflex such as we have been describing. If an older child 
sucks his thumb or bites his nails, we say that he has a bad 
habit. A reflex is an act such as every normal person would 
perform under the same conditions; usually it is clearly bene¬ 
ficial. A habit is an act which only particular persons per¬ 
form; it may be helpful or harmful, attractive or unbecoming. 


















5 2 


PHYSIOLOGY AND HEALTH 


Desirable habits have the value of reflexes which were just 
mentioned; that is, they make a great part of our behavior so 
easy and natural — ‘second nature/ as we say — that we 
are given a chance to think about other things. When a very 
young boy is putting on his clothes, he cannot think of any¬ 
thing else unless he stops dressing. When he is older, he 
dresses more easily and can think of other things while he is 
about it. He puts his fingers on a button and at once his 
muscles begin to work it through the buttonhole. His nerv¬ 
ous system goes ahead making the necessary connections, but 
the act is one which had to be learned; it did not take care of 
itself when it was first tried. 

Perhaps this has given you some idea of the difference be¬ 
tween the nervous system in a very young baby and that in a 
child a few years older. The baby has all his muscles in 
working order. All his sense organs, too, are united with 
his brain by sensory nerve fibers, probably the full number. 
But the brain has not made the connections that must be made 
to the muscles if they are to respond to all the changes that 
affect the eye, the ear, and all the other instruments of the 
senses. The connections, of course, have been made for a 
few needful reflexes, but only gradually are other connections 
built up — ‘coordinations’ made, if you want to use the word 
physiologists use — so that a greater variety of actions be¬ 
comes possible. 

Memory. — There are two things especially to be kept in 
mind when we think about the brain. In the first place, it is 
arranged to make connections between the sense organs and 
the muscles. This suggests once more the idea of reflex ac¬ 
tion. In the second place, it is changed in the course of its 
use. Everything that happens to us seems to make the brain 


THE NERVOUS SYSTEM 


53 


different in some way from what it would have been if the 
particular adventure had not occurred. Since every one has 
his own experiences and they are different from those of any 
one else, as time goes on he grows more and more distinctly 
himself and comes to differ even from his twin brother. 



Eye 

Motor 


Trige¬ 

minal 


Audi¬ 

tory 

(Hear¬ 

ing) 

Pneu- 

mogas- 

tric 

Motor 


Optic 

(Sight) 


sory 


Facial 

(Face 

motion) 


THE BASE OE THE BRAIN SHOWING THE ORIGIN OF NERVES 


Because everything that happens to us thus leaves a more 
or less lasting impression in the brain, we can say that the brain 
is the organ of memory. We can recall many incidents in 
our past lives and much that we have read. Of course, no¬ 
body else can recollect exactly the same matters in exactly the 






54 PHYSIOLOGY AND HEALTH 

same way. Each man’s brain seems in some respects like a 
library in which he has stored his diaries and notebooks. He 
can search among them and find records of things that took 
place long ago. Some brains seem to be in better order than 
others, so that questions in regard to the past can be more 

Cerebrum 


MIDSECTION OE THE BRAIN 

The brain has been cut through the center to show the right half. 

regularly and surely answered by their owners. In some 
cases it seems as if the books were in sad disorder. We call 
the owners of such libraries forgetful. Disease may act 
like a fire or some other calamity to damage these precious 
collections. 

The brain. — The brain of a grown man is a mass of tissue 
weighing about three pounds. The spinal cord goes down 



THE NERVOUS SYSTEM 


55 


from the brain through an opening at the base of the skull 
and continues through a tunnel made by the arches of the 
bones of the spine. Nerves leave it in pairs, one going to the 
right and one to the left, reaching all parts of the trunk, arms, 
and legs. There are also nerves (twelve pairs) which enter 
or leave the brain itself. Most of these are connected with 
structures in the head, like the eye and the ear. 

By far the largest part of the brain is what we call the 
cerebrum . It is divided into right and left halves almost $s 
sharply as a walnut kernel. Its surface is very much 
wrinkled and of a gray color. Inside it there is a mass of 
nerve fibers closely packed together and running in all di¬ 
rections. 

It is the wrinkled surface of the cerebrum which is of spe¬ 
cial interest. It is made up of what is called ‘gray matter.’ 
You may have heard this expression used as though it stood 
for ‘intelligence.’ The microscope does not tell us much 
about it except that it is a very complex mass of nerve cells. 
But we know that when we learn, this gray matter is changed 
and developed. 

The gray matter spread over the surface of the cerebrum 
is related to the fibers underlying it somewhat as the switch¬ 
board in a telephone exchange is related to the wires and 
cables that come to it and go from it. If such a switchboard 
were to be torn down, we should see the broken ends of thou¬ 
sands of wires. If the gray layer were removed from the 
surface of the brain, we should expose the cut ends of millions 
of nerve fibers, too small to be seen by the naked eye. The 
telephone wires lead electric signals into the switchboard 
where connections are made so that other wires may lead them 
out again. In a similar way various nerve fibers conduct 


PHYSIOLOGY AND HEALTH 


5 6 

nerve signals into the gray matter of the brain and others 
conduct signals away from it. Both in the brain and in the 
switchboard the connections are constantly being shifted. 
We do not know just what it is that the nerve fibers are carry¬ 
ing. It is not an electric current as commonly understood, 
nor a pulse of some strange fluid as was once believed. We 
have said that the fibers convey signals. The scientific term 
for them is impulses. 

There has been much discussion as to whether or not dif¬ 
ferent parts of the cerebrum have to do with particular powers 
of mind and body. A hundred years ago many persons 
thought that the brain surface could be mapped out quite 
definitely; that each region had its own service to perform. 
This was a very attractive idea, but we know now that most 
of these claims were wrong. No faith, therefore, can be 
placed in the advertisements we sometimes see even today 
which picture a man’s head with labels like ‘language/ ‘con¬ 
structiveness/ and ‘cautiousness’ on different areas. And 
no faith can be placed in the claims of those who pretend to 
determine a person’s abilities by feeling the bumps on his 
skull. What we do know about the special uses of parts of 
the surface gray matter is shown in the diagram on page 58. 

The muscles which bend your right arm are put in action 
by means of nerve fibers coming to them from the spinal cord 
in the neck. But this part of the cord is under control of the 
cerebrum. It is known that when such a movement of the 
arm is carried out, the impulses come down into the cord from 
a very definite locality. The locality in the brain is, roughly 
speaking, above the ear, and it is interesting to learn that it is 
on the side of the head opposite to the muscles which are set 
to work. If the right arm is the one that is raised, then the 


THE NERVOUS SYSTEM 57 

part of the brain definitely used at this moment is on the left 
side. We call the part used the motor area for the arm. 

If it had been the leg rather than the arm that you had 
chosen to move, the motor area used would have been higher 
up on the brain surface — just the opposite of what you might 
have expected. If the movement had been made by the lips, 
the center would have been below that for the arm. A num¬ 
ber of these motor areas can be definitely located on the sur¬ 
face of the cerebrum. If we go back to the comparison 
between this layer of gray matter and the telephone switch¬ 
board, the conditions may suggest that the connections for a 
certain part of the city are close together on the board. This 
is a very probable arrangement. 

Just as there are regions of the brain surface which have 
particularly to do with the government of muscles, so there 
are others which are used for receiving impulses from other 
parts of the body. A good example is found in the eyes. A 
large nerve comes from each eye into the interior of the skull 
and there joins the brain from below. The fibers of these two 
optic nerves can be traced into the lower parts of the brain 
from which paths are provided to bring the impulses into the 
back part of the cerebrum. It has been known for a long 
time that disease or wounds of this part of the brain may 
cause blindness. The eyes might then be all right, but their 
nerve fibers would have lost their useful connections. They 
would be like telephones after a fire had destroyed the central 
station. 

Since you have read that the muscles of the right side are 
governed from the left half of the cerebrum, you may sup¬ 
pose that the right eye also connects with the left half of the 
cerebrum. This is true in many of the lower animals, but 


PHYSIOLOGY AND HEALTH 


58 

not in man. The arrangement is not so simple; the left half 
of the brain is concerned with what is to the right of the ob¬ 
server, whether he is using one eye or both. 

There is evidence that other sense organs, for example the 
ear, are associated with special areas in the brain to which 


MOTOR AREA 



DIAGRAM OF THE BRAIN SHOWING THE SUPPOSED LOCATION OF 
SPECIAL ACTIVITIES 

their impulses, or signals, are chiefly sent. But some parts 
of the cerebrum are not directly connected with any sense 
organ, and we cannot label them clearly to show just what 
services they perform. 

Between the cerebrum and the spinal cord there is a part 
of the brain which has to do with many important activities 
of the body that go on without any conscious control on our 








THE NERVOUS SYSTEM 


59 


part. Our breathing, the regulation of the circulation of the 
blood, and the government of the organs of digestion are all 
controlled from this small space. All that is between the 
cerebrum and the cord may conveniently be spoken of as the 
brain stem. 

The cerebellum is a part of the brain stem which has greatly 
interested students. It is a rather large outgrowth toward 
the back, just under the hind part of the cerebrum. You 
might take it to be a portion of this mass, but it is not. Dis¬ 
ease of the cerebellum does not interfere with intelligence, 
but with the smoothness and success of muscular movements. 
We have described such movements as being governed from 
the cerebrum. In general they are so governed, but the 
centers of the cerebellum seem to cooperate in a helpful way. 
When a battalion parades under the orders of a single com¬ 
manding officer, the perfection of the performance depends 
very much on the captains, lieutenants, and guides, who set 
the distances and see to it that each movement is made at the 
right instant by each group of soldiers. The cerebellum 
seems to have an influence of just this kind. It secures what 
is called Coordination of movement.’ 

Sleep. — We spend about one-third of our lives in the state 
which we call/sleep.’ Not much has been learned about this 
condition; it is hard to say just what makes the difference be¬ 
tween lying still to imitate sleep and really sleeping. When 
we wish to sleep' we protect ourselves against anything that 
might disturb or even interest us. We turn off the light and 
close our eyes. We try to have quiet surroundings. We try 
to relax comfortably so that there will be no such flow of im¬ 
pulses from the muscles up to the brain as when we are keep¬ 
ing our balance. The eye, the ear, and the muscles are for 


6o 


I 


PHYSIOLOGY AND HEALTH 


the most part off duty. The pressure on the surface of the 
body is soon unnoticed if we do not move restlessly, but keep 
quite still. 

Even when we have in these ways reduced as much as pos¬ 
sible the streaming of sensory impulses to headquarters, we 
may not succeed in sleeping, for we must also tone down our 
mental state, much as we protected the body from disturb¬ 
ance. What finally happens to make us unconscious of our 
surroundings, we do not know exactly. The deepest sleep 
comes in the first two hours of the night. This has been 
proved by experiments that show that it takes louder noises 
or stronger electric shocks to wake persons during this time. 

You can see that many parts of the body have a chance to 
rest and be renewed while you sleep. This is true of most of 
the muscles, most of the central nervous system, and of its 
allied sense organs, especially the eyes. Breathing and the 
beating of the heart must still go on, but at a lowered rate. 
Digestion probably proceeds as usual; we know that many 
animals sleep immediately after eating heavily. One of the 
wonderful facts about the condition is this: if the sleeper has 
‘something on his mind,’ as we say, a responsibility of some 
sort, he will often waken at very slight sounds if these are re¬ 
lated to his particular interest. A change in the baby’s 
breathing may wake the mother when a passing fire engine 
has failed to do so. 

Probably there are lazy persons who sleep more than is 
necessary, actually wasting time in this way. This is not 
the common fault with boys and girls. They find life so ex¬ 
citing that they dislike to miss pleasure by sleeping; they are 
inclined to cut into the period which ought to be given up to 
sleep. When it seems impossible to get up in the morning, it is 
time to fix an earlier hour for going to bed. 


THE NERVOUS SYSTEM 


61 


The autonomic nervous system. — The most interesting 
activities of the body which we can see are certainly those of 
the muscles. You know now that there is an invisible activity 
of the cells and fibers of the nervous system which sets the 
muscles to work. A large part of the brain is busy with this 
regulation. But another large section of the nervous system 
is devoted to the control of organs which are not so distinctly 
subject to the will. We cannot determine how rapidly the 
heart shall beat or how fast the intestine shall push onward 
its contents. We cannot command the blood to go in in¬ 
creased quantity to a particular region. We cannot make 
the numerous glands secrete more or less of their products 
simply by willing such changes. All these adjustments and 
others like them are said to be made through the autonomic 
nervous system. 

The word ‘autonomic’ is probably not familiar, but you have 
heard the word ‘automatic/ which means self-acting. The idea 
is much the same. Our skeletal muscles are not self-acting, 
but require a special order from headquarters to make them 
execute each movement. The heart, the glands, and all those 
organs in which the simple smooth muscle is present, do have 
some automatic action. From time to time the autonomic 
nervous system may cause this activity to increase or dimin¬ 
ish. We shall find many illustrations of such influences when 
we study the circulation and digestion. 

Discussion 

1. What are the functions of the nervous system? 

2. How does the nervous system protect the body? 

3. What part of the body might be paralyzed by a fracture of 

the skull on the right side? Explain. 


62 


PHYSIOLOGY AND HEALTH 


4. Of what use to the body are reflexes? 

5. What activities of the body, besides the movement of volun¬ 

tary muscles, are controlled through the nervous system? 

6. What is meant by calling the brain the ‘organ of memory’? 

7. Discuss the structure of the brain. 

8. Discuss the structure of nerves. 

Experiments 

1. Observe the knee jerk. 

2. The ‘reaction time’ may be measured by the old method of 

finding how long it takes a squeeze to be passed from hand 
to hand around a circle of pupils. Divide the total time 
by the number taking part. 

3. With a pair of compasses find out how widely the points must 

be separated to be felt as two on different parts of the skin 
(finger tips, back of hand, neck). It is better t$ have an¬ 
other person set down the compasses on your skin while 
your eyes are closed. Both points must touch the skin at 
the same moment. 


V 


THE SENSE ORGANS 

How do you know what is going on in the world around you? 

How does a baby learn about the world? 

Of what use are internal sensations in the baby and in later life? 

Do you receive more than one type of sensation through the skin? 

How is one’s balance maintained? 

How is it that one is able to see distant hills and then a near-by 
printed page? 

Do you know what it means to be far-sighted, near-sighted, color¬ 
blind? 

How does one hear? 

Kinds of sensation. — When we were describing the nerv¬ 
ous system, we said that some of its fibers carry impulses in¬ 
ward and that all we ever learn of the world and our com¬ 
panions we owe to these fibers. For example, the optic nerves 
connecting the eyes with the brain enable us to see, and the 
auditory nerves connecting the ears with the brain enable us 
to hear. 

Children are usually told that there are five senses: sight, 
hearing, smell, taste, and touch. Each of the first four has 
its own apparatus, distinct from that of the others; but the 
term ‘touch’ is generally used to include all the sensations 
which come from the skin, and this is not a very satisfactory 
use of the word. We get from the skin the feeling of cold and 
the feeling of warmth, for instance, and each of these depends 
on a particular set of nerve fibers. 

63 


6 4 


PHYSIOLOGY AND HEALTH 


There are many sensations which we think of as associated 
with the condition of our bodies. The list of ‘five 
senses’ does not include a place for these; a headache, for in¬ 
stance, is something outside the list of five. You see that 
the five senses have to do with recognizing things outside our¬ 
selves, but we must often attend to feelings which depend on 
what is happening within. It is well to distinguish two classes 
of sensations, the internal and the external, so that we may in¬ 
clude all kinds. 

Most internal sensations are painful or at least disagree¬ 
able. They are usually signs of conditions which need to be 
changed in some way. Since hunger is unpleasant, it stimu¬ 
lates us to secure food; if it were delightful, we should not 
want to put a stop to it. Pains generally call our attention 
to conditions that are not normal and that need correcting. 
Unfortunately, the way to correct the difficulty is not always 
as clear as it is in the case of hunger. 

Impulses which make us conscious of internal sensations 
must travel over nerve fibers leading from the various organs 
to the brain. Presumably such impulses arise when con¬ 
ditions in the organs are peculiar. Thus, it is known that 
when a man is so hungry that he feels gnawing pains, each 
pang is associated with a tightening of the muscular walls 
of the empty stomach. He feels this involuntary contrac¬ 
tion much as he might feel a cramp in the muscles of his leg. 
When the stomach has been filled with food, only the lower 
end of it contracts, and these contractions seem to arouse 
no sensations. 

Sensations from the skin. — Among the cells of the deeper 
layers of the skin are vast numbers of nerve endings, which 
provide external sensations. We speak of them as ‘nerve 


THE SENSE ORGANS 


65 

endings’ though they are more truly ‘nerve beginnings.’ 
They serve as feelers, as do the whiskers of the cat or the 
antennae of the butterfly. When anything presses upon the 
skin, these fine twigs of the nervous system are affected, and 
impulses are sent to the cord and brain. If a patch of the 
skin is chilled, another set of endings is there to respond to 



SENSE ORGANS OF TASTE 


A, map of the upper surface of the tongue showing on the left the 
different kinds of papillae and on the right the areas of taste. (After 

Hall) Area sensitive to bitter (-); to acid (.); to salt 

(—.—.—.—); to sweet (-). B, section through a papilla; 

n, small nerve connecting with taste buds at d; e, epithelium. C, single 
taste bud magnified: n, nerve, the fibers of which terminate between the 
spindle-shaped cells a; e, epithelial cells. 

this form of stimulation; if it is warmed, there is still another. 
If the skin is more roughly treated — pricked or cut or 
burned — a fourth set of endings becomes active, and as a 
result pain is felt. 

Some parts of the skin are better supplied with endings of 
one sort, others with endings of another sort. We have the 
sense of touch best developed in connection with the finger 
tips, the lips, and tongue. Temperature is more successfully 





66 


PHYSIOLOGY AND HEALTH 


judged at other places, the elbow for instance. Pain is per¬ 
haps most easily produced when something touches the cornea 
(the bulging part of the eyeball). 

Our sensations are the result of changes in the body and in 
the outside world affecting the brain through the sensory 
nerves. These changes may be of several different kinds. 
Some are mechanical, as in the case of the true sense of touch, 

Olfactory Bulb.-,. 

Olfactory Nor Yes.-- 

Branches of_ 

fifth Merve. 

Turbinated Bones 


NERVES OF THE OUTER WALL OF THE NASAL CAVITY 
The nerves of smell are those at the top of the figure (olfactory nerves). 

where it is pressure which starts the impulses. It is also a 
mechanical disturbance which makes us hear, a rapid vibra¬ 
tion carried from the air to the beginnings of the auditory 
fibers in the internal ear. 

Taste and smell.—Other changes are chemical. The nerve 
endings are excited by chemical substances brought in contact 
with them. If salt is placed on the tongue it dissolves in the 
saliva and then reaches the fine branches of nerve fibers which 
are stimulated by it. In addition to salt, we recognize sweet, 






THE SENSE ORGANS 


67 

sour, and bitter substances. Each quality depends upon 
special nerve endings. Those endings which respond to sweet 
substances are most numerous at the tip of the tongue. Bitter 
substances are tasted at the back of the tongue, while taste 
buds for salt and sour substances are most numerous along 
the sides. There is an area on the top of the tongue which is 
practically free from taste buds. Probably we obtain sensa¬ 



tions of smell because the odorous material has reached the 
upper part of the nose and there become dissolved in the 
moisture which is upon the lining. It is surprising to find 
how little of some compounds is sufficient to give an odor. 
We commonly experience taste and smell at the same time and 
fail to distinguish between the two sensations. 

The eye. — The eye and the ear are the two sense organs 
which have the most remarkable machinery. Of these two, 






68 


PHYSIOLOGY AND HEALTH 


the eye is better understood and more easily described. The 
eyeball is a globe about an inch in diameter. Among all 
parts of the body this is nearest to having its future size in a 
newborn baby. It is so placed as to be very well protected 
from injury. It takes up most of the space in the deep hol¬ 
low, called the orbit, which is so noticeable in a skull. The 
strong ridge of the brow juts out to shelter it. Behind the 
eyeball there is a fatty cushion; in front there are the lids. 

The two lids can be brought quickly and tightly together 
over the front surface of the eye. When they are closed, there 
is a slit between the lids and the eye, and into this chink the 
tears are discharged. Tears come from a collection of small 
glands under the overhanging brow. They drift, over the 
surface of the eye, cleansing it by their flow, and at the inner 
angle of the lids they are drained into the nose. So it happens 
that an extra secretion of tears is followed by the presence of 
moisture in the nostrils and by snuffling. 

A very thin and delicate membrane lines the lids and covers 
all the exposed part of the eyeball. This is called the con¬ 
junctiva. Inflammation of this membrane is a common and 
disagreeable condition. It is called conjunctivitis or, more 
familiarly, pink eye, and is due to an infection. The 
remedy is to give the eyes a rest, to bathe them often, and to 
keep a cloth soaked with boracic acid solution upon them 
when lying down. They should not be rubbed. 

There are six slender muscles attached to each eyeball. 
By their nicely balanced action they can turn it to various 
positions. These muscles are so controlled by the brain that 
the two eyes usually work together with great precision. If 
they do not do this, we have the disagreeable experience of 
seeing double. The eye muscles are very active, much more so 


THE SENSE ORGANS 


69 


than we realize until we take pains to watch the signs of their 
play in other people. When the eyes are directed, first at one 
part of an object and then at another, we secure information 
about it much like that gained when we handle the article; we 



are forming an idea of the relative position of its parts, or 
surfaces. 

The eyeball may fairly be called a little camera. In order 
to do its work a camera must be so made as to keep out the 












70 


PHYSIOLOGY AND HEALTH 


light everywhere except at one opening. The camera is black 
on the inside to guard against the reflection of stray light. 
Similarly in the eye light enters through a single opening, the 
pupil. The lining is not black, to be sure, but it is quite dark. 
The pupil is a hole of variable size, widening to make the most 
of dim light and contracting when the light is unusually 
strong. These changes in the size of the pupil are brought 
about by the action of muscle cells in the colored ring, the 
iris, which surrounds it. In this respect the iris is very like 
the diaphragm, or stop, of the camera which we adjust ac¬ 
cording to the amount of light available for the taking of each 
picture. 

The light entering a camera goes through a lens or a com¬ 
bination of lenses, with the result that a picture is produced 
on the plate or film. The lens combination in the eye in¬ 
cludes (1) the bright, clear cornea which makes the front 
surface of the eyeball, and (2) a second lens which is behind 
the pupil. One important difference between the eye and an 
ordinary camera is the fact that the camera has air inside, 
while the eye is filled with a transparent jellylike material. 
The retina of the eye is in the position of the film in the camera. 
It contains thousands of peculiar cells having an orderly ar¬ 
rangement like the stones in a pavement or like the minute 
yellow spikes which are crowded together in the center of a 
daisy. 

Accommodation. — To make a sharp picture in a camera 
we have to attend to the focus; that is, we have to make 
changes in the distance between the lens and the back of the 
box until the picture is clear. In the eye, too, an adjustment 
must be made for the particular things we wish to see. An 
eye which is normal has a clear picture of distant objects on 


THE SENSE ORGANS 71 

its retina when no special effort is being made. But it must 
accommodate to see clearly what is close at hand — the page 
of a book, for instance. This act of accommodation does not 
consist in lengthening the eye, as would be done with a camera, 
but in changing the form of the lens concealed behind the 
pupil. The lens, when we look at a near object, becomes 
more strongly curved. You can easily convince yourself 
that when near objects are clear, distant ones are indistinct. 
Stand near a window and look out through a wire screen. 
You can choose whether you shall see the screen clearly or 
the houses across the street. You cannot see them both 



CHANGES IN THE LENS IN ACCOMMODATION 


clearly at once; when you gain a good picture of either, the 
other is blurred. 

The power to accommodate is greatest in little children 
and is gradually lost in later life, because the lens becomes 
more and more rigid. A time comes to persons with aver¬ 
age eyes when glasses have to be used for reading. These 
glasses are curved out ( convex ), so that when they are put on, 
the effect on the eye is just the same as though the lens inside 
were made rounder (more convex), as it used to be when these 
persons were younger. 

People are said to be near-sighted when they have eyes in 
which the retina is farther back from the lens system than it 




72 


PHYSIOLOGY AND HEALTH 


should be. They can see certain things close by without any 
effort to accommodate, but they cannot see things at a dis¬ 
tance unless they put on proper glasses. They have to wear 
concave (curved inward) lenses. In later life they may take 
off their glasses to read instead of putting them on. There 
are cases of farsightedness in which the eye is not so deep as 
it needs to be. Convex glasses are helpful to the far-sighted. 

Center of vision. — When light stimulates the cells of the 
retina, it causes chemical changes something like those re¬ 
sulting from the influence of light on a photographic film. 
Near the middle of each retina there is a spot which is superior 



Far-sighted Eye 


Normal Eye 



Near sighted Eye 


DIAGRAM SHOWING DEFECTS OF EYESIGHT 
The far-sighted eye is too shallow. The near-sighted eye is too deep. 


to all the rest in its usefulness. When we say that the eye 
is fixed upon an object, we mean that the image, or picture, 
of the object is fixed upon this central spot. For instance, 
when we read, we move the eyes in such a way that the letters 
and words fall on centers of clear vision. Things which are 
imaged on parts of the retina outside the spot of best vision 
are indistinct, and the farther they are from the middle, the 
more indistinct they are. When one of these indistinct images 
attracts our attention, as it may do by moving, we instantly 
shift the eyes so that the new object of interest comes to 
occupy the center of vision. 














THE SENSE ORGANS 


73 

Color vision. — Our sense of color as well as of form is at 
its best at the middle of the retina and is lost toward the out¬ 
side. Tests can be made to show that we can see objects 
whose images are far from the center of the retina without 
being able to judge their color at all. There is a region of the 
retina not so far out in which we can recognize blue and yel¬ 
low, but not red and green. Some persons have this in¬ 
ability even at the center of the retina, and they are said to be 
color-blind. You can see how serious it would be for an 
engineer or a pilot not to be able to tell these colors apart. 
With modern traffic signals all drivers of automobiles need 
this ability. 

Stereoscopic vision. — If you were to be asked why it is 
better to have two eyes than one, you might be inclined to 
answer that two eyes can see more. This is not so good an 
answer as that two eyes can see better. You do not see much 
more of the landscape when you have both eyes open than 
when you use only one, but you have a more exact knowledge 
of the shapes and positions of the various objects. This is 
difficult to explain, but it is connected with the fact that the 
right and left eyes see things from slightly different angles. 

If you wanted to learn the exact shape of a box, you could 
view it first from one place and then from another. Compar¬ 
ing the two impressions would help you to make up your mind 
as to its real form. Since you have two eyes, you can really 
see the box or any other object from two points at once. Even 
though the two points of view are only three or four inches 
apart, we are greatly helped by the combined effect. This is 
what is called stereoscopic vision. If you have seen stereo¬ 
scopic photographs, you know how they make you feel that 
certain parts of the scene are close by and others far away in 


74 


PHYSIOLOGY AND HEALTH 


the background. Such pictures are made from two separate 
points. Then the right eye is forced to see just what it 
would when looking at the real object and the left eye just 
what it would see. 

Probably one of the first things a baby has to learn is to 
judge the location or direction of the objects that make images 
on his retinas. Apparently he learns to do this by practice. 
He is at first excited by what he sees, but he cannot reach in 
the right direction to grasp it. Soon he learns to do this with 
success. His brain has become organized so that the eyes 
can command the arm muscles. You can easily realize how 
much of our education is along this line. Learning to bat a 
ball is a more complex process of the same kind; your muscles 
promptly answer to what your eyes see as the ball flies to¬ 
ward you. 

The ear. — What we generally call the ‘ear 5 is only the 
strangely shaped projecting part serving to some extent to 
gather in those vibrations of the air which give us our sensa¬ 
tions of sound. The real organ of hearing is deeply hidden in 
one of the bones of the skull. The ear passage which dis¬ 
appears into the head leads into this bone. The rapid pulses 
of air are conducted to the inner end of the passage where 
they affect a delicate membrane which is stretched across it. 
This is what people generally mean when they speak of the 
‘drum 5 of the ear, though it is the drum-head rather than 
the drum. It is called by the anatomists the tympanic mem¬ 
brane. If you are listening to a tuning fork which is sound¬ 
ing middle C, the fork is vibrating 256 times in a second and 
so is the tympanic membrane. 

Behind the tympanic membrane there is a small, irregular 
space filled with air and corresponding to the inside of a drum. 


THE SENSE ORGANS 


75 

A slender passage, the Eustachian tube, connects this cavity 
with the upper part of the throat at the back of the nose. 
This connection is valuable because it keeps the air pressure 
on the two sides of the tympanic membrane from becoming 
seriously unequal. When you go rapidly to the top of a very 
high building, you may feel discomfort in the ears or even be¬ 
come a little deaf. The outside air at the high level has less 



DIAGRAM OF SECTION THROUGH THE HUMAN EAR 


pressure than that down below; in going up in the elevator, 
you have taken with you, in the space behind the tympanic 
membrane, a sample of the lower and denser air, and this 
pushes out the drum-head. But if you remember to swal¬ 
low, that opens the Eustachian tube and at once relieves you. 
If you have a severe cold, you may have a similar difficulty 
in hearing because the Eustachian tube is swollen and does 
not open properly when you swallow. 









76 


PHYSIOLOGY AND HEALTH 


The space within the membrane is called the middle ear. 
It contains a chain of three tiny bones. Taking these in order 
from the outside inward, the first (the hammer) is at¬ 
tached to the tympanic membrane and vibrates with it. This 
bone is linked to the second (the anvil), and this in turn to 
the third, which is called from its shape the stirrup. The 
stirrup fits into an opening which is the beginning of what is 
called the internal ear. 

This is a very winding and much divided space in the bone, 
into which enter the many thousand fibers of the auditory 
nerve. The internal ear does not contain air, but instead a 
clear watery fluid. The vibrations of the tympanic mem¬ 
brane are carried by the chain of bones across the middle ear 
and passed on to the liquid contents of the deeper regions. 

Sound. — If we think again of the tuning fork, we may 
picture its vibrations reproduced in the bones within the 
middle ear and finally in the fluid with which the nerve fibers 
have close relations. Just what happens in the internal ear 
is uncertain, but it is generally believed that certain nerve 
fibers are excited in response to a particular vibration rate — 
like the 256 per second of the tuning fork — and others by 
other vibration rates corresponding to higher and lower 
pitches. Many sounds, of course, do not have exact pitches 
which we can recognize; they are mixtures or they are rapidly 
shifting pitches and therefore excite a number of different 
nerve fibers. 

Defective hearing. — Deafness may be caused in many 
different ways. A simple case, easily cured, is that in which 
the waxy secretion of the outer passages has collected in such 
large amounts as to check the action of the ear drum. No 
one but a skillful physician should attempt to remove such an 


THE SENSE ORGANS 


77 


accumulation. The tympanic membrane may be pierced 
with a small opening without making the patient deaf, but 
further injury may interfere with hearing. Obstruction of 
the Eustachian tubes may make trouble, as already pointed 
out. Sometimes the little bones in the middle ear lose their 
freedom of movement. Or the difficulty may be still deeper 
— in the internal ear, the nerve, or the brain itself. 

The sense of balance. — Closely connected with the ear 
are some curious and interesting structures called the semi¬ 
circular canals. These are not concerned with hearing, but 
are supposed to be useful in aiding us to keep our balance. 
From them arises also the sense of dizziness or giddiness when 
we are in positions like high places, where we are likely to 
lose our balance. The unpleasant symptoms of seasickness 
are, for example, set up by the unusual stimulation of the 
semicircular canals when we are tossed about on a boat at 
sea. In some of the lower forms of life, in the fish for ex¬ 
ample, the semicircular canals are large and important, much 
more so than the organ of hearing. This we would naturally ex¬ 
pect to be the case, because the fish has little need for being 
sensitive to vibrations but much need of knowing the positions 
of his body as he swims in various directions through the 
water. 


Discussion 

1. What is a sense organ? 

2. Do we have sensations when there is no stimulation of nerve 

endings? How about dreams? 

3. Give examples of mechanical stimulation, of chemical stimu¬ 

lation, of temperature stimulation, of light stimulation, 

4. What kinds of sensations are set up in the skin? 


78 PHYSIOLOGY AND HEALTH 

5. What is the use of pain? 

6. What sensations are set up in the mouth? 

7. Do we confuse taste and smell? 

8. Describe the eye. 

9. What is meant by accommodation? 

10. What is the trouble with a near-sighted eye? 

11. What can people do to avoid eye strain? 

12. What is the value of sleep for the sense organs? 

13. Discuss the rules of hygiene for the eye and the ear. (See 

appendix.) Can your class improve in following these 
health practices? 

14. Why are we unable to see at first when going from a very 

bright room into a dark room? 

15. How is the eye moved? 

16. Explain what we mean by the middle ear. Describe it. 

17. How is it possible for the middle ear to become infected? 


Experiments 

1. Look out the window. Can you see the glass in the window 

and a distant object at the same time? Explain. 

2. See whether you can observe a difference in the size of the 

pupil of another person’s eye when he is looking in differ¬ 
ent directions. Explain the results of your observations. 

3. Feel the rough surface of some object with the tips of the 

fingers and then with the back of the hand. Keep the 
eyes closed during each test. In which case could you tell 
the nature of the rough surface more exactly? Explain 
why. 

4. With a clean knife cut small pieces from the inside of an 

apple which is neither distinctly sweet nor sour and from 
the inside of a potato. Hold the nostrils tightly together 
with one hand and see whether there is the usual sharp 



THE SENSE ORGANS 79 

difference in taste between these two substances. Explain 
the result. 

5. Study the results of tests for vision and hearing which were 

last made upon your class. 

6 . Much that is true of the eye can be illustrated by means of a 

camera having a ground-glass back. Near-sightedness and 
far-sightedness with their correction by concave and convex 
lenses can be made entirely clear if simple lenses are at 
hand. 

7. Note the difficulty of standing steadily with the eyes closed, 

especially on one foot. This demonstrates the part played 
by the eyes in keeping one’s balance. 


VI 


THE HEALTH OF THE MIND AND 
NERVOUS SYSTEM 

Do the brain and nerves get tired? 

Do they need special care? 

Does the health of the body affect the mind? 

Does the action of the mind affect the various functions of the 
body? 

What is a healthy mind and how can it be secured? 

The living structure of the central nervous system. — 
You remember that the entire nervous system is made up of 
living cells, each with a central body containing a nucleus and 
with fibers which carry impulses, messages, or stimuli. Some 
of these fibers are several feet long, others only a quarter of 
an inch. But all nerve fibers depend upon the health of the 
cell body from which they grow, and they are unable to live if 
they are cut off from this body or if it is destroyed. The 
nervous system, through this network of remarkable cells 
and fibers, controls our movements, the processes of digestion 
and secretion, and the process of thinking, itself. 

The emotions, too, are activities of the nervous system. 
The impulses which accompany joy, sorrow, anger, or other 
emotions may be so numerous as to flood all the ‘ telephone 
lines’ and thus quite take possession of the nervous system. 
We speak of a person being ‘blind with rage’ or ‘dumb with 

80 


HEALTH OF MIND AND NERVOUS SYSTEM 81 


grief/ meaning that the nervous system is so given up to 
these emotions that the person is incapable of intelligent sight 
or speech. 

Simple physical habits develop through the establishment 
of well-marked paths in the central nervous system. It has 
been explained that the process of dressing becomes almost 
automatic, because one condition calls for the next action. 
The impulse from each condition moves along the right path 
and results in the next movement. We see then that we train 
the nervous system so that it comes to act in the same way 
under the same conditions and this constitutes a habit. 

In your study of memory you learned that some record is 
left in the cell structure of the brain from each experience. 
We make associations between things which happen at the 
same time. For example, the name and the face of a person 
are so recorded in our experience that when the name is men¬ 
tioned in the absence of the person, we can recall his appear¬ 
ance. Here again we see a definite relation between what 
has happened to the cells of the nervous system (what stimuli 
they have received) and the way in which our minds work. 

Since, then, our various activities, including thought and 
emotion, are developed through living nerve cells and their 
relationships, it is clear that the care of these living cells is of 
prime importance. Like other cells of the body, they become 
tired and function less well when overused or abused. When 
we are nervously tired, we get fretful, are easily annoyed, and 
think less clearly. 

Concentration. — Only one thought can completely oc¬ 
cupy the mind at one time. When we are rested we are bet¬ 
ter able to keep our attention upon our work and to disregard 
messages which are being sent to the brain from outside 


82 PHYSIOLOGY AND HEALTH 

stimuli. When the cells of the brain are tired, we are less 
able to do this. 

Rest for the cells of the central nervous system is provided 
by sleep, which puts an end to the thinking process, or by 
change of work, which rests certain cells by calling other 



AN UNHAPPY MENTAL STATE 


groups of cells into action in their place. Just as the muscles 
of the hand which have become tired through writing have a 
chance to rest when we are walking, so one group of cells in 
the brain has a chance to rest when we stop one kind of men¬ 
tal work and give our attention to another. 

You can usually control the conditions of both work and 



HEALTH OF MIND AND NERVOUS SYSTEM 83 

rest. It is easier to do mental work when the eyes and ears 
are not sending messages to the brain from sights and sounds 
which are in no way connected with the thing you are doing. 
Keep on your desk only the books and materials you are 
working with at the time. Keep the work place as quiet as 



A HAPPY MENTAL STATE 


practicable. When you are sleeping at night, you will rest 
better if the bedroom is quiet. You may not wake up com¬ 
pletely because of noises in the street, but they do disturb 
you. You will be more rested in the morning if you have 
slept soundly and undisturbedly. 

The cells of the nervous system, like other living cells, 





8 4 


PHYSIOLOGY AND HEALTH 


demand proper care. This includes correct living, sufficient 
sleep, fun, and relaxation, and proper vacations from daily 
routine. 

The health of the body affects the central nervous sys¬ 
tem. — Since the living cells of the nervous system are re¬ 
sponsible for all sensations of the body, including those of 
pain, it follows that lack of health in any bodily organ will 
usually make itself felt in the nervous system. Pain, like the 
emotions of fear and anger, sends messages to the nervous 
system which so control its action as to prevent it from con¬ 
tinuing even such important functions of the body as diges¬ 
tion. You know, too, that constipation and other digestive 
difficulties make one feel depressed and make the mind less 
alert. 

It is plain, therefore, that you should have physical defects, 
like defects of the eyes or teeth, corrected if you are to give 
your mind the best chance to do its work. Such defects are 
not only bothersome in themselves, but they also interfere 
with general health and with mental health. 

We have various evidences of the effect produced upon 
the cells of the brain by poisonous substances in the blood. 
In certain diseases like typhoid fever, for example, where the 
temperature is high and bacterial poisons are present in the 
system, the patient is often delirious. His mind acts quite 
abnormally. 

Alcohol also prevents the proper functioning of the cells of 
the brain. When this substance is present in the blood, abil¬ 
ity to think accurately is reduced. If enough alcohol is 
taken, the control of the mind and nervous system is entirely 
lost. A man gradually recovers his mental capacity as the 
alcohol gets out of the system; but if he uses alcoholic liquor 


HEALTH OF MIND AND NERVOUS SYSTEM 85 

immoderately, he continues to injure the nerve cells until the 
injury becomes permanent and alcoholic insanity may result. 

Possibly you may have noticed various other conditions 
which illustrate the effect of the body upon the mind. When 
the body has undergone a long illness, the mind is likely to be 
depressed rather than cheerful. You know how fussy a baby 
gets when he is overtired. You have probably been so tired 
yourself that you found it difficult to remain good-natured. 
You may have had a headache which made you thoroughly 
uncomfortable and interfered with your ability to do mental 
work. The headache arose from some wrong condition in the 
body, perhaps from indigestion or eyestrain, but it seriously 
interfered with the work of the mind. The living cells of 
the central nervous system are sensitive to the general health 
of the body. A healthy body which is well cared for makes 
it easier to have a healthy mind and nervous system. 

The effect of mental conditions upon the body. — You 
have already learned something of the nature of the auto¬ 
nomic nervous system. You have seen that it causes certain 
things (like weeping, blushing, and changes in blood supply) 
to take place without the control of the will. Yet there is 
such a relation between the autonomic system and the brain 
that impulses from either one can pass over to the other. 
Worry, which is really a mild sort of fear, interferes with 
digestion. A poor digestion, through its general effect upon 
the body (including the nerve cells), makes one feel more 
despondent and still more like worrying. Thus a poor con¬ 
dition of the mind not only makes for the poor functioning of 
the body, but it also reacts upon the mind itself. 

If one were foolish enough to do so, he could let his mind 
dwell upon worry and anger until he made himself feel so 


86 


PHYSIOLOGY AND HEALTH 


miserable that the condition interfered with his general body 
functions. This interference would come through the dis¬ 
turbance of his normal nervous control and through the secre¬ 
tion of various products from the ductless glands. Indeed a 
reasonably well person might actually think himself into a fit 
of illness and an ill person would certainly be better if, instead 
of thinking of his illness, he would center his mind on pleasant 
and interesting things. 

An example of the effects of mind upon body is seen in the 
condition which is called neurasthenia (weak nerves). In 
this condition the nervous system has been overworked or 
reduced to a lowered state of health through the ill effects set 
up by continued worry or bodily defects. Such a person is 
dissatisfied with everything about him. He is extremely 
sensitive. Impulses play over the nervous system without 
normal control. He feels that the room is too light or too 
dark, too noisy, too hot or too cold. He feels warm and then 
chilly; the heart is irregular. He is likely to pity himself 
and has very little regard for the feeling of others. If the 
mind can be centered upon something interesting and worth 
while, many of these harmful effects upon the body cease and 
the person feels, and is, in much better health. 

Developing a healthy mind. — Let us turn our attention to 
the mind and its development. Certainly we want a healthy 
mind as well as a healthy body, but perhaps we do not find 
‘healthy mind’ so easy to define. What are some of the 
characteristics of mental health and how may they be se¬ 
cured? 

We must recognize, of course, that minds vary just as bodies 
do. Some have better minds and can do more difficult mental 
work than others, just as some have better bodies and can do 


HEALTH OF MIND AND NERVOUS SYSTEM 87 

more difficult physical work, like athletic stunts, than others. 
Different minds are not equally good at the same kind of 
work. We say that a person is adapted to a given kind of 
work when his mind does the work well. The man who is 
engaged in work for which he is suited is usually happy. The 
selection of the right kind of work is a matter of great im¬ 
portance. 

Whatever the nature of our work, however, we need the 
quality of mental health. By this we mean the ability to use 
the mind effectively and satisfactorily. One element of 
mental health is the ability to get on with other persons, and 
this is a most important part of good training. The healthy 
mind meets various situations with success; it avoids fear and 
worry, and it has an interest in life which brings contentment 
and happiness. Let us see what habits we can develop which 
contribute to mental health. 

We develop habits of thinking in a certain way just as we 
develop habits of walking in a- certain way. We can, for 
example, develop the habit of concentration or we can come 
to lack this valuable ability. If we try hard to keep our minds 
upon our work and crowd out other thoughts, we can gradu¬ 
ally increase our ability to do so. If, on the other hand, we 
allow our minds to wander and to think about every new idea 
which suggests itself, we lose that power of concentration 
which has been shown to be an important characteristic of 
most successful people. 

Sights and sounds are always trying to make their way into 
the center of consciousness, so that it is only by keeping them 
out that we can train the mind to do effective work. It is 
equally important when we are playing that we refuse to 
think about our work. If we carry the worries of our studies 


88 


PHYSIOLOGY AND HEALTH 


to the playground, we do not get the mental rest during sports 
that we ought to have. Complete relaxation demands that 
the mind shall have the ability to disregard thoughts about 
other things than the game in hand, just as the ability to work 
well demands the power to disregard suggestions outside the 
particular job. Fondness for one’s work is a factor in de¬ 
veloping good concentration, and this shows again the reason 
for selecting a line of work which one enjoys. The training 
of the mind to develop the habit of concentration is of great 
importance. 

You will think of other habits of mind. You know some 
persons with whom cheerfulness is a habit and others who are 
habitually fault-finding, selfish, and bad-tempered. Habits 
like these go to make up personality. 

Personality. — The dictionary definition of personality is 
“that which constitutes distinction of person; distinctive per¬ 
sonal character; individuality.” When you think of the 
personalities of your friends and say that so-and-so has a 
pleasing personality, you mean that he has the habit of being 
cheerful, friendly, honest, interesting, and sympathetic. 
These are qualities of mind that can in some measure, at 
least, be produced by training. The friends you like best have 
the qualities of mind which have just been listed. These 
friends have good minds and they have trained them in 
the right direction. 

When we say that a person is an optimist, we mean that he 
has the habit of thinking of the best and most cheerful side 
of every situation. When we say that another person is a 
pessimist, we mean that he characteristically thinks of the 
worst side of any situation. Perhaps you have heard the 
homely rhyme which goes: 


HEALTH OF MIND AND NERVOUS SYSTEM 89 

’Twixt optimist and pessimist the difference is droll; 

The optimist the doughnut sees, the pessimist the hole. 

This is intended to suggest that no matter how simple the 
situation may be, these two types of persons have trained 
themselves in habits of thought so that one will see the best 
feature, the other the worst. 

Similarly one could develop the habit of being either selfish 
or friendly. A selfish person has the what-am-I-going-to- 
get-out-of-this habit. The friendly person has the how- 
does-the-other-fellow-feel-about-this habit. You know which 
kind of person you want for your friend, and that tells you 
which habits you ought to develop yourself if you are go¬ 
ing to make friends. 

The development of the right kind of personality is, then, 
highly important. A person who is angry may run or he may 
fight; he may cry or he may smile. Sickness makes some 
persons disagreeable, but others are cheerful in spite of it. 
The rich are not all cheerful nor the poor all sad. Clearly 
the mind is superior to these conditions, and each mind must 
have principles of operation of its own. The characteristic 
manner of behaving for each mind is developed through habits 
of thought. 

Control. — Let us see what are some of the principles of 
controlling the mind and developing right mental habits. A 
baby frets itself into a rage because its hand gets caught under 
the blanket, but as soon as its attention is called to something 
else it forgets all about its trouble and begins to laugh. If 
the mind can be fully occupied by only one thought at once 
and things annoy us only when we let them, then we can 
crowd out worry if we will but think about something else. 


go 


PHYSIOLOGY AND HEALTH 


Most of the things we worry about never happen anyway; so 
why should we not think of something pleasant instead of 
worrying? When we are suffering from worry, our minds do 
not work logically and we cannot think clearly or be fair to 
others. Fear and worry are certainly enemies to our peace 
of mind, and we will do well to find out how to overcome 
them. 

Another principle for developing mental health is to learn 
to enjoy many things — sports, games, music, nature, fishing, 



CAMPFIRE GIRLS LEARN THE JOY OF OUTDOOR ACTIVITIES 


reading. Get a hobby. Learn to do something well with 
your hands. Nothing is more restful when you are mentally 
tired than to leave the mental work and turn to some kind of 
hand work which you do very well. 

Another principle of mental health is to accept the inevi¬ 
table. What good does it do, for example, to fuss about the 
weather? You cannot change it; so you may as well be 
cheerful yourself and allow other persons to be cheerful by 
accepting what comes. 




HEALTH OF MIND AND NERVOUS SYSTEM 


91 


Of course, things do not always go your way, but it is worth 
a great deal to ‘keep a stiff upper lip.’ If you force your¬ 
self to smile once when things are going wrong, the smile will 
come easier next time, and you soon come really to feel the 
way you had to pretend to feel at first. Self-reliance is a 
wonderful quality. A baby does not have it; great leaders 
do have it. It is the ability to carry through, come what 
may. It is confidence in one’s self and the determination to 
do the best one can no matter what difficulties appear. 

Summary. — We can train the mind by forming right 
habits of thinking so that we take the right point of view of 
whatever situation may arise. If we train our minds in the 
right way, we shall have the kind of personality that will make 
us happy, and that will enable us to get on happily with 
others. There are many characteristics of mental health 
which might be listed: happiness; productive work; social 
adaptation; contentment; cheerfulness; confidence; courage; 
calmness; faith; serenity; freedom from any tendency to be 
nervous, quarrelsome, sensitive, or touchy; lack of tendency 
to be angry, cruel, or boisterous; unwillingness to find excuses 
for one’s self; truthfulness; unwillingness to blame others; 
ability to give a fair value of others’ opinions; lack of tend¬ 
ency to be conceited, vain, timid, or lazy; power of concen¬ 
tration; an interest in the world about one; pleasure in com¬ 
panionship; cooperation; being on good terms with the world 
and with the people in it; interest in games and recrea¬ 
tion; thoughtfulness and consideration; unselfishness; alert¬ 
ness. 

One writer on personal hygiene says that there is no better 
statement of the principles of mental health than that in 
Kipling’s “If”: 


92 


PHYSIOLOGY AND HEALTH 


If you can keep your head when all about you 
Are losing theirs, and blaming it on you; 

If you can trust yourself when all men doubt you, 

But make allowance for their doubting, too; 

If you can wait, and not be tired by waiting, 

Or being lied about, don’t deal in lies, 

Or being hated, don’t give way to hating, 

And, yet, don’t look too good, nor talk too wise — 

. . . you’ll be a Man, my son! 

Discussion 

1. Discuss the value of the following precepts: 

Never cry over spilled milk. 

Tackle one job at a time. 

Nothing is so bad but that it could be worse. 

Nothing can annoy you unless you let it. 

2. Tell in your own words what the following proverbs mean in 

relation to mental health: 

“He that keepeth his mouth keepeth his life, but he that 
openeth wide his lips shall have destruction.” 

“A soft answer turneth away wrath, but grievous words 
stir up anger.” 

“Better is a dinner of herbs where love is than a stalled ox 
and hatred therewith.” 

“Pride goeth before destruction and a haughty spirit be¬ 
fore a fall.” 

“He that is slow to anger is better than the mighty and he 
that ruleth his spirit than he that taketh a city.” 

“A merry heart doeth good like a medicine, but a broken 
spirit drieth the bones.” 

“A man that hath friends must show himself friendly.” 

“Seest thou a man diligent in his business? He shall stand 
before kings; he shall not stand before mean men.” 


HEALTH OF MIND AND NERVOUS SYSTEM 


93 

“He that hath no rule over his own spirit is like a city that 
is broken down and without walls.” 

“The wicked flee when no man pursueth, but the righteous 
are bold as a lion.” 

“Wine is a mocker; whoever is deceived thereby is not 
wise.” 

3. What differences of mind and body are apparent in the pic¬ 

tures on pages 82 and 83? 

4. Discuss the following Code of Sportsmanship: 1 

Keep the rules. 

Keep faith with your comrade. 

Keep your temper. 

Keep yourself fit. 

Keep a stout heart in defeat. 

Keep your pride under in victory. 

Keep a sound soul, a clean mind, and a healthy body. 

Play the Game. 

Experiments 

1. See how many minutes you can study without any outside 

thought entering your mind. 

2. Keep a record for a few days of situations which demand self- 

control. See whether you meet them wisely. 

3. Try putting some worry or thought out of your mind by think¬ 

ing of something else. Can you stop the tune that is Tun¬ 
ning in your head’ ? 

4. Make a list of the different qualities of personality which you 

have observed. 

5. Make a list (for the sight of no one except yourself, your 

parents, or a good friend) of the qualities of personality 
you believe you possess. 


From Sportsmanship, November, 1928. 


VII 


THE MECHANICS OF THE CIRCULATION 

How many quarts of blood are there in the body ? 

What does the blood carry in its constant course over the body? 

What is the clotting of blood and how is it useful? 

How does the circulation of blood help to keep the body temper¬ 
ature even? 

What gives blood its red color? 

What is the usefulness of the white blood corpuscles? 

What makes the pulse which you can feel in your wrist? 

Every one knows that whenever the skin is cut blood conies 
in sight. In the whole body of a grown man there is about a 
gallon of this liquid and it is in constant motion. It is said to 
‘circulate.’ This means that the blood is passing over a 
certain route and coming again and again to the same places. 
It is kept moving by the pumping action of the heart. 

The circulatory system. — The heart is really a pair of 
pumps, although you could not see that it has a right half and 
a left half just by looking at it. Each half is a force pump 
and drives blood out through branching tubes which are called 
arteries. The arteries from the right side of the heart go to 
the lungs. Those from the left side reach all the other parts 
of the body, even the most distant, like the hands and feet. 
The blood which has been sent from the right side of the heart 


94 



MECHANICS OF THE CIRCULATION 


95 


to the lungs finds its way back to the left side by way of tubes 
which are called pulmonary veins. Other veins (systemic 
veins) collect the blood from every other region and conduct 
it back to the right side of the heart. A study of the diagram 
will help you to understand the plan of the circulation. 



You will see that blood which has been to a particular place, 
such as the head, cannot return to this place without having 
visited the lungs in the meantime. This arrangement makes it 
certain that the blood arriving in all the organs will be fully 





















9<5 


PHYSIOLOGY AND HEALTH 



I Aorta, 


m Free aval 
Vein 


IV Postcaval 
Vein 


Gastric Artery 
Splenic Artery 
Hepatic Artery 
Pancreatic 
Artery 


Renal Vein 
Renal Arteries 


Iliac Arteries 
Iliac Veins 


DISTRIBUTION OF ARTERIES AND VEINS 

































MECHANICS OF THE CIRCULATION 


97 


stocked with oxygen which it has gathered in the lungs. In a 
complete circulation the blood passes through the heart twice, 
first through the one side and then through the other. 

Arteries branch as they are followed away from the heart. 
The branches become finer and more numerous until they 
cannot be traced by the eye. There was a time, even after 
the facts of the circulation had become well understood, when 
it was a mystery how the blood passed from the finest arteries 
into the neighboring small veins. Just how this was possible 
could not be known until the microscope showed the minute 
structure of the tissues. By the aid of this instrument it was 
made out that there are extremely short and slender passages 
which unite the smallest arteries to the smallest veins and so 
transfer the blood from one to the other. These passages are 
the capillaries. The name means ‘hairlike,’ but capillaries 
are generally much finer than hairs. A single capillary seems 
an insignificant affair, but it is to be remembered that these 
tiny vessels are exceedingly close together and that their 
number is almost beyond imagination. They bring the blood 
near to all the cells of the body. 

Arteries and veins have walls of some thickness, but capil¬ 
laries are made of the thinnest sort of cells arranged in a single 
layer. This layer is an example of delicate epithelium. The 
service of blood to the living tissues could not be performed 
unless the capillaries were thin enough to allow dissolved 
substances to pass through their walls. Oxygen must es¬ 
cape through these thin walls and so must dissolved food. 
Waste materials from the tissues must enter the blood through 
the same thin walls. In the case of the capillaries of the 
lungs the exchange of substances is the opposite of the one 
just described, because in the lungs the oxygen is entering 


PHYSIOLOGY AND HEALTH 


into the blood and an important waste — carbon dioxide — 
is passing out of the blood to be removed in the breath. 

The nature of the blood. — Most persons probably think 
of the blood as a red and somewhat sticky fluid. You may 
have heard the saying, “Blood is thicker than water.” As a 
matter of fact, it really flows very freely in the vessels through 
which the heart sends it, and the idea that it is thick and 
sluggish comes from the fact that we usually see it when it is 
undergoing the curious change 
known as clotting. When blood 
reaches the air, it generally becomes 
solid in a short time. This is a 
very fortunate thing, for this clot¬ 
ting closes small wounds before the 
loss of blood has been serious. 
Then the clot dries and becomes a 
scab, which is a shield under which 
the healing process can go on. 

One of the commonest mishaps 
is a nosebleed. The blood vessels 
in the lining of the passages between the nostrils and the 
throat are very close together and carry far more blood 
than would be found in a similar area of the skin. The 
capillaries are also very near the surface. This arrangement 
is necessary to insure the protection of this lining against cool¬ 
ing and drying by the passing air currents. Of course, such a 
surface is easily broken. The mucus secreted by the cells 
of this membrane often dries upon it and forms a crust. 
When this crust is dislodged by vigorously blowing the nose 
or by the bad practice of picking at it, the underlying tissue 
may be torn and blood may flow freely. A nosebleed may 



CAPILLARIES IN THE WEB 
OF A FROG’S FOOT 


(Greatly Magnified. From 
Hall’s Physiology.) 



MECHANICS OF THE CIRCULATION 


begin suddenly without any evident reason when some weak¬ 
ened patch of the nasal lining gives way. 

If the bleeding is from just within the nostril, it may some¬ 
times be checked by pressing on the upper lip. Cold water 
applied to the nose is almost always helpful. It is well to 
rest quietly while getting over a nosebleed, for any exertion 
leads to a more active circulation in the injured tissue and 


tends to force more blood 
through it. There are some 
unfortunate persons whose 
blood does not have much 
tendency to clot when it is 
shed. When this condition 
(hemophilia) exists, a nose¬ 
bleed may be very difficult 
to control and even danger¬ 
ous to life. 

The redness of blood is 
due to the presence in the 
blood of microscopically 
small bodies which are red 
when seen in considerable 
masses. These minute colored bodies are the red corpuscles. 
A single one is extremely small. It might take six or seven 
in a row to reach across the cut end of a hair, but the whole 
number is so great that the red corpuscles occupy nearly half 
the space in any volume of blood. As seen under a micro¬ 
scope they appear as tiny discs. Often they are seen to 
stack themselves in piles like those one makes when count¬ 
ing coins. They are so crowded together that it seems 
strange that the blood is not like mud. But the corpuscles 



RED BLOOD CORPUSCLES 

It would take seven red blood 
corpuscles to re^ch across the cut 
end of a fine hair. 



100 


PHYSIOLOGY AND HEALTH 


are soft and yielding; they change their shape under pressure 
and spring back again when they are free to do so. The 
capillaries in the body are so narrow that the corpuscles have 
to pass through them in single file. The red corpuscles are 
formed in a rather unexpected place, the marrow of the 

bones. The red material 
of which they are largely 
composed is called hemo¬ 
globin. 

The service of the 
hemoglobin in the red 
corpuscles is the carrying 
of oxygen between the 
lungs and the living tis¬ 
sues. This gas, received 
from the air which we 
breathe, is constantly 
needed. Ordinary liquids, 
water for instance, have 
very little power to dis¬ 
solve oxygen, though even water can hold enough to keep 
fishes alive. Hemoglobin gives to the blood the capacity to 
hold a great deal of oxygen. The blood absorbs this neces¬ 
sary gas while it is passing through the capillaries of the 
lungs, and a few seconds later it gives it out through the 
walls of the capillaries in all parts of the body. The quan¬ 
tity of oxygen in blood determines its color. The fully 
charged blood is bright red; when it loses part of its oxygen 
it becomes darker, and if it should lose all, it would be 
nearly black. Usually less than half of the oxygen which the 
blood offers to the tissues is taken up by them. Our veins 




MECHANICS OF THE CIRCULATION 


look bluish as we see them through the skin, but the color of 
the blood within them is not so different from that in the 
arteries and capillaries as many suppose. 

The gallon of blood in the body of a man can absorb some¬ 
what less than a quart of oxygen. When a man is at rest, 



(Greatly Magnified) 


White Corpuscles 



he requires about half a pint of oxygen every minute. If he 
takes exercise, he may need ten times as much or even more. 
At such times a great deal more blood than usual is driven 
through the capillaries of the muscles, and more oxygen is 
taken from the blood by the muscle tissues. 

When one first looks at a drop of blood under the micro¬ 
scope, it seems as though the corpuscles were all of one 




102 


PHYSIOLOGY AND HEALTH 


kind. Most of them are the sort which we have been talking 
about, the red cells which are the carriers of oxygen. But 
we may also discover cells of another type, the white cor¬ 
puscles, as they are called. In comparison with the red 
corpuscles their number is very small; there may be only one 
white corpuscle to five hundred or one thousand of the red 
corpuscles. 1 Yet the white cells of the blood are of great in¬ 
terest and importance. Most of them appear much like 
certain cells which are found living free in the water of pools 
and ditches. They have a definite power of movement and 
can change their shape. The soft protoplasm of which they 
are composed can take in various particles which come in con¬ 
tact with it. If such particles are good food for the cells, 
they may be dissolved and lost sight of within. We say that 
they have been digested and become part of the cells which 
have devoured them. The white blood corpuscles, by an ac¬ 
tion of this kind, may remove bits of foreign substance from 
the blood and in particular destroy some germs which cause 
diseases. 

The liquid part of the blood is called the plasma. It can 
be separated from the corpuscles and is then seen as a clear 
yellowish fluid. It makes up slightly more than half the 
volume of the blood. The chemists have found it to be rich 
in food substances which are on their way from the organs of 
digestion to other places where they may be needed. This 
is what we should expect. We might also anticipate that the 

1 The blood count as carried out in a laboratory shows that the normal 
blood in man contains about 5,000,000 and in women about 4,500,000 red 
blood corpuscles per cubic millimeter. There are about 10,000 white blood 
corpuscles per cubic millimeter, although the number is variable. Remember 
that a cubic millimeter is about the volume of a large grain of granulated sugar. 


MECHANICS OF THE CIRCULATION 103 

plasma would contain waste material on its way to organs 
like the lungs and the kidneys through which such matter can 
be removed. It does in fact contain a surprisingly large quan¬ 
tity of carbon dioxide gas which will presently escape by way 
of the lungs. Other substances which can be recognized as 
wastes are kept down to a remarkably low level in the blood. 

Another task which the blood has to do is connected with 
the distribution of heat. This is something which we do not 
often think about. Where oxygen is being used by living 
cells, there is always some heat produced, just as heat is set 
free in the burning of a candle or a coal fire. You know that 
the body is kept warmer than the outside world at all times 
save in the hottest summer weather. It is the burning, or 
oxidation, of materials made from our foods which provides 
this heat. Some parts produce much more heat than others. 
The muscles at work develop most of the heat. So the blood 
which goes through an active muscle must be heated as it 
passes on its way and be rather warmer in the veins of the 
muscle than in its arteries. A little later it will share the heat 
supplied by the muscle with other tissues of the body which 
have not been manufacturing heat so freely. 

You will understand that in this way the circulating blood 
helps to keep a nearly even temperature in different parts. It 
may remind you of the hot water which moves through the 
pipes and radiators used to heat a house. This water is first 
heated in the furnace. If it remained there, it would grow 
hotter and hotter while the rooms upstairs might be cooling 
off. But it is always circulating, like the blood, and the sys¬ 
tem is generally so well managed that the cellar, where the 
furnace is, does not get warmer than the rest of the build¬ 
ing. 


104 


PHYSIOLOGY AND HEALTH 


The part of the blood which is most cooled must be that 
which comes close to the surface of the body. The skin loses 
heat to the air, so that the blood flowing through the veins of 
the skin is certain to be cooler than the blood in most other 
veins. This cooled blood will soon be mixed with other blood 
which has come from places under the surface and which has 
a higher temperature. As the two are blended, the stream 


To Head and Arms 



THE HEART AS SEEN FROM THE FRONT 

will have about the average temperature which it is best that 
it should keep. Besides losing heat through the skin, the 
blood which circulates in the walls of the air passages is some¬ 
what cooled by the breath. 

We can now sum up the services of the blood somewhat in 
this way. It carries oxygen from the lungs to the active or¬ 
gans. It brings them food from the intestine or from places 
where it has been in storage. It takes away from the active 
tissues the wastes which they are forming. Among these the 
most abundant is the gas, carbon dioxide, which is taken to 



MECHANICS OF THE CIRCULATION 105 

the lungs where it is allowed to escape. The blood also helps 
to regulate the temperature. 

The heart. — The heart lies nearly in the middle of the 
chest. It is about as large as its owner’s fist and weighs some¬ 
thing like three-quarters of a pound. The arteries and veins 
join it above; the lower end is somewhat pointed and the tip 
is to the left. It comes close to the wall of the chest, where 



THE HEART AS SEEN FROM BEHIND 

you can feel it as it hardens with each beat. The place where 
this throb is felt is between the fifth and sixth ribs (counting 
down from the top). 

It has been said already that the heart is really a pair of 
force pumps. When it is opened, it is found that the hollows 
of the two halves, right and left, are completely separated. 
Each half consists of two divisions, or chambers, which are 
connected by an opening. On either side the upper cham¬ 
ber, the auricle receives blood brought into it by the veins. 
Thence the blood goes down into the lower chamber, or ven¬ 
tricle. A great artery arises from each of the two ventricles. 


106 PHYSIOLOGY AND HEALTH 

The auricles have thin walls; the ventricles are much more 
strongly built, especially the left. They do the chief work 
of the heart. 

The heart is composed of muscle of a peculiar kind. The 
cells of this muscle are arranged 
in bundles which are wrapped 
around the cavities of the ven¬ 
tricles in curious curves. When 
all these curved bundles contract 
at once they squeeze strongly 
upon the blood in the ventricles, 
and it is thus forced out through 
the arteries. The hollows may 
be almost completely closed, so 
that scarcely any blood remains 
in them. Then the muscle soft¬ 
ens and the blood flows in from 
the auricles, filling the space 
which is made for it as the walls of 
the ventricles separate more and 
more. 

All force pumps are made with 
valves which allow the liquid to 
go only in one direction. The 
heart is constructed on just this 
plan. There are thin, but strong, flaps reaching down into 
the ventricles, which move apart to let blood come down 
from the auricles, but which are brought tightly together 
when the ventricles begin to press on their contents. When 
this pressure is applied, the blood cannot slip back toward 
the veins through which it came in. It can leave only through 



MUSCLE FIBERS OF THE 
HEART 

(Greatly Magnified) 

This shows the cross mark¬ 
ings, divisions, and junctions 
of the muscle fibers. The 
nuclei and cell junctions are 
shown only on the left-hand 
side of the figure. 












MECHANICS OF THE CIRCULATION 107 

the arteries, the route from the right ventricle to the lungs 
and from the left ventricle to the body in general. 

In the beginning of each of the two great arteries there is 
a second set of valves. These valves are in the form of small 
pockets, three in a set. The loose edges of the pockets are 
turned away from the heart, 
so that when the blood is 
shot out, the flaps are laid 
close against the lining of the 
arteries. The moment the 
heart ceases to push the blood 
into the arteries, the three 
pockets bulge until their edges 
come together and block the 
passage. Each ventricle, then, 
has two sets of valves associ¬ 
ated with it, the first to admit 
blood from the auricle and the 
second to let it into the ar¬ 
tery. The strong pressure of 
the ventricle during its con¬ 
traction keeps the first set 
firmly closed, but holds the 
others open for the passage of 
the blood. 

The two ventricles act at the same time and the same 
amount of blood is driven out by each — about half a tumbler¬ 
ful when a man is sitting still, but as much as a whole tumbler¬ 
ful when he is taking heavy exercise. When a man is at rest, 
the rate of the heart may be something like 60 beats a 
minute, but it may speed up to 150 when he is running. If 



CAVITIES AND VALVES OF THE 
HEART 


The right side of the heart as it 
appears when dissected to show 
cavities and valves. B. Right 
semilunar valves. 


io8 


PHYSIOLOGY AND HEALTH 


you think it over, you will see that if the rate does go up from 
60 to 150 and twice as much blood is put out at each beat, the 
quantity sent on its way each minute when the man is hard 
at work will be jive times as much as when he is resting. 

The ventricles supply almost all the force which is used in 
keeping up the circulation, but the thin-walled auricles play 
a certain part in the heart’s activity. Just before each 
powerful contraction of the ventricles there is a quick and not 
very energetic contraction of the two auricles. This hap- 

Auricle 

Curtainlike 
valves 


Pocketlike 

valves 

Ventricle 


DIAGRAM OF THE HEART SHOWING THE ACTION OF THE VALVES 

pens at a moment when the ventricles are already pretty well 
stretched by the entering blood and the effect is to pack down 
into them a little more blood. 

You know that the total amount of blood in the body is 
about a gallon. If the quantity thrown into the arteries by a 
single beat of each ventricle is a half-tumblerful, or a gill, 
then in about 32 heartbeats it would seem that all this blood 
should go twice through the heart; that is, once through the 
right half and once through the left half. But this may not 
be quite accurate, for we must remember that some of the 








MECHANICS OF THE CIRCULATION 


109 




the heart cut to show the thickness of the ventricle 

WALLS 








no 


PHYSIOLOGY AND HEALTH 


paths within the circulation are very much longer than others. 
A corpuscle that happens to enter an artery leading to the 
shoulder will probably be back in the heart long before one 
which chances to find its way to the foot. The shortest 
possible way by which any blood can pass over from the left 
side of the heart to the right is through the vessels of the 
heart itself. Arteries are provided which begin just outside 
the valves at the exit from the left ventricle. They conduct 
blood to the capillaries in the muscular walls of the heart 
and then it passes through veins directly into the right auricle. 
A good blood supply is absolutely necessary to keep the 
heart in working order. 

Although the heart does the main work in keeping the blood 
in motion, it has some help from outside which ought to be 
mentioned. The veins of the arms and legs are provided 
with simple valves which are the same in principle as those of 
the heart. That is, they let the blood pass along in one di¬ 
rection but will not allow it to reverse its flow. When a man 
is walking, the veins of his legs are pressed between the 
muscles or between the muscles and the skin and squeezed 
at every step. Each time the pressure falls upon a vein which 
is full of blood, it is flattened and emptied. On account of 
the valves, the emptying is always toward the heart. Then 
when the muscles soften again the flattened veins refill, but 
only from the tissues, never by blood flowing backward. 
This action of exercise has been spoken of as a ‘milking’ of 
the veins. It helps greatly in lifting the blood from below 
toward the level of the heart. 

Strong quick breathing movements, such as are made by a 
man who is running, also help on the circulation. Every 
time the chest is expanded room is made in it for extra blood. 


MECHANICS OF THE CIRCULATION m 

When the chest is being enlarged, the lower part of the body 
is pressed upon by certain muscles and so blood from the 
large veins of the abdomen is hurried on its way toward the 
right auricle. 

The arteries and the veins. — The arteries are strong elas¬ 
tic tubes and they carry blood which is under high pressure. 
They are firm to the touch because of this pressure, and di¬ 
rectly after each heartbeat they are momentarily given an ad¬ 
ditional stretch. This pro¬ 
duces the throb which is best 
felt at the wrist, and which 
we call the pulse. If an ar¬ 
tery is cut, the blood springs 
forcibly from it, and the jet 
leaps higher with the throb of 
the pulse, lessening between 
the beats. The blood in the 
arteries not only presses 
harder after each sudden out¬ 
pouring from the ventricle but also darts forward for a mo¬ 
ment at an increased speed. 

The elasticity of the arteries is important. If a force 
pump is made to drive liquid through rigid tubes (metal or 
glass) there is a complete standstill between strokes and then 
the whole body of fluid must be put in motion again. More 
power is required than with an elastic system. If the tubes 
can stretch, some of the liquid sent into them will find room 
by widening them momentarily. An instant later, when no 
delivery is being made by the pump, the elastic walls will be 
closing in again and sending onward some of the stored fluid. 
There is no standstill in this case. 



Open Shut 

VALVES OF THE VEINS 













112 


PHYSIOLOGY AND HEALTH 


As a man grows older, his arteries lose their elasticity. 
The loss is more marked in some persons than in others of the 
same age, but it seems bound to occur in every one. It may 
remind you of the stiffening of the lens in the eye. We speak 
of the change as ‘hardening of the arteries, 5 or arterioscle¬ 
rosis. As the vessels harden, they also tend to be somewhat 
narrowed and to become crooked. The task of the heart is 

made more difficult. The 
channels resist more and 
more the passage of blood, 
and there is a serious loss 
of momentum between the 
heartbeats. The pulse is 
then felt as a rather star¬ 
tling shock. To get enough 
blood through the arteries 
under these conditions the 
heart must develop peaks of 
very high pressure, and thus it is called upon to work harder 
at a time when it is naturally losing strength. Sooner or later 
the heart may fail. 

Normal arteries are very strong, but the hard arteries of 
old persons may be brittle. As the blood pressure in them 
leaps high with every pulse, there is increasing danger that 
some fragile artery will be broken. If such a rupture occurs 
in the brain, the escaping blood may do so much damage as to 
cause sudden death. With less serious bleeding, partial paral¬ 
ysis may result. 

The flow in the arteries is so rapid that the longest blood 
journeys, as from the heart to the foot, are made in a few 
seconds. The return through the veins is also very swift. 



A CROSS-SECTION OF A SMALL 
ARTERY AND A VEIN 





MECHANICS OF THE CIRCULATION 


ii3 

The blood in the veins, however, is under but little pressure 
and it moves steadily rather than by pulses. If a vein is cut, 
a large amount of blood will escape, but the bleeding is more 
easily controlled than that from an artery. 

The movement of the blood through the capillaries from 
the small arteries to the small veins has been watched with the 
microscope. The rate of progress is extremely slow com¬ 
pared with that in the arteries and veins. It may be as little 
as one six-hundredth of the speed in the larger arteries. The 
result is that a corpuscle may take as much as a second to pass 
through a capillary which is only a twenty-fifth of an inch in 
length. It is well that this is so. If the blood were shot 
rapidly through the capillaries, it might not have time to give 
up much of its oxygen or to take in much of the carbon dioxide 
offered to it. It would reach the veins but little altered from 
its condition in the arteries. This would not be getting good 
service from each portion of the blood. On the other hand, 
if the flow through the capillaries should be much slower the 
blood might be so changed as to be of no further use before 
moving away from the locality. 

The portal system. — You have learned to think of the 
blood from any organ as being gathered into veins which bring 
it back to the heart. There is one region of the body where 
the plan is different. This is the digestive system. The 
blood which has been in the walls of the stomach and intestine 
is collected by many veins and these finally unite in one. It 
would be expected that this would empty into the great vein 
which passes up from below to reach the right auricle, but 
it does not do this directly. It disappears into the liver. 
Within this large organ this vein, called the portal vein, breaks 
up into branches, and the blood is finally led through micro- 


PHYSIOLOGY AND HEALTH 


114 

scopic passages which are much like capillaries. These join 
to form a second set of veins, and the blood finally returns to 
the heart. 

It will be seen that the blood from the digestive tract is 
made to pass close to the cells of the liver before it is permitted 
to go to any other part of the body. The portal vein, you will 
notice, is like other veins in the way it begins, but it is rather 
like an artery in the way it ends. No other large vessel be¬ 
haves in this way, though there are some small ones in the 
kidney which do the same thing; that is, they begin by the 
joining of small vessels but end by dividing again into others. 
Many centuries ago the Greeks discovered the close connec¬ 
tion between the intestine and the liver and concluded that 
the food passed to this organ to be made into blood. This is 
not exactly the way we should express it, but it is true that 
most of the food absorbed takes its course through the portal 
vein and may be affected in various ways by the liver. 

Discussion 

1. Discuss the parts or elements which go to make up the blood. 

2. Why do we speak of the circulation of the blood? 

3. Of what tissue is the heart made? 

4. Discuss the structure of the heart. 

5. What determines the rate at which the heart beats? 

6. Discuss the action of the valves which allow the blood to flow 

in only one direction. Compare the structure of these 
valves with a mechanical pump. 

7. Name the services of the blood. 

8. Discuss the speed with which blood flows in different parts 

of the body. 

9. Describe the portal system. 


MECHANICS OF THE CIRCULATION 


US 


Experiments 

1. Buy a beef heart or sheep heart at the market if possible and 

study its structure in the class. 

2. Count the number of heartbeats as indicated by the pulse in 

a half-minute when you are sitting still. Hop twelve times 
on one foot and then take the pulse again. 

3. If you have a microscope at school, put a drop of blood on a 

clean glass slide and examine it under the microscope. 


VIII 


THE CONTROL OF THE CIRCULATION 

How is blood sent to a part of the body where it is most needed? 

What changes in the circulation of the blood take place when 
some region of the body becomes infected? 

What is lymph and what is its usefulness? 

How is it possible for a runner to get extra oxygen during a race? 

Circulatory adjustments. — There are many wonderful 
things about the circulation. One of the most remarkable, 
which we do not often stop to think of, is the fact that it all 
works so smoothly when the position of the body is changed. 
When you lie in bed, the blood is sent in proper quantities to 
all parts; when you stand up, this is still the case. If you 
think what would happen in any sort of model of the system, 
you will see how marvelous this really is. In an artificial 
model made of rubber and the size of the body a fluid repre¬ 
senting blood might be pumped around evenly so long as the 
figure lay horizontally, but think what would happen when it 
was set up on end. All the tubes in the lower part would be 
stretched and those in the upper part would grow smaller. 
The proportion of the liquid above and below would be very 
different from what it was before. 

How the settling of blood in the lower levels of the system 
is prevented is too difficult to explain here. When a man is 
in good health, a number of reflex adjustments are made to 

116 


CONTROL OF THE CIRCULATION 


117 


guard against it. But when a man is sick enough to be con¬ 
fined to his bed, these adjustments are not working so well. 
If he attempts to get up quickly, then the blood settles away 
from his head, somewhat as it would do in the model, the brain 
suffers from a lessened supply, and he may faint. A reduced 
flow of blood through the brain is what causes fainting. Such 
a reduction may result from weakened heart action under the 
influence of some nervous shock. At other times the heart 
may not be at fault; the chief trouble may be that the blood 
is too largely collected in some other part of the body. When 
severe indigestion makes one feel faint and weak, there is 
probably a great accumulation of blood in the organs of the 
abdomen so that a lessened allowance is available for other 
regions. 

What has just been said ought to remind us that the system 
we are talking about is a living one and so able to make fre¬ 
quent changes. We are not likely to forget that the heart is 
alive, but we should also remember that the small blood ves¬ 
sels are alive, too. As a matter of fact, the small arteries and 
veins have many living muscle cells in their walls. Thus they 
can contract and relax, sometimes closing down on the blood 
which is flowing through them and sometimes opening more 
widely and allowing a freer passage. 

Nerves and blood vessels. — The heart and the blood ves¬ 
sels are connected with the nervous system, but the heart does 
not have to be prompted by the brain to make it beat; it can 
go on after all its nerves have been cut. Nevertheless its 
beating is regulated from time to time by means of these 
nerves. The relation between the brain and the heart is 
something like that of a driver to his horse. The animal can 
go along pretty well by himself, but he is often held back or 


n8 


PHYSIOLOGY AND HEALTH 


hurried by his master. We think of the reins as serving to 
restrain the horse when necessary and of the whip as a means 
of urging him on. The heart has two distinct nervous con¬ 
nections which may correspond the one to the reins and the 
other to the whip. 

There are certain nerve fibers which come from the lower 
part of the brain and can be traced down the neck into the 
chest and finally to the heart itself. It is known that these 
fibers act like the reins in our comparison. Indeed, in some 
animals, as frogs and turtles, the heart nerves can act in such 
a way as to stop the heart and keep it at rest for long periods. 

Other nerve fibers come to the heart by a roundabout way 
from the upper part of the spinal cord. Their influence is 
like that of the whip upon the horse. The heart is driven to 
its best performance when the checking nerves cease to 
restrain it and the stimulating nerves urge it on. This is 
what happens during vigorous exercise when, as already 
pointed out, the rate of the beat may be more than doubled 
and the amount of blood sent out at each stroke greatly in¬ 
creased. 

The circulation meets special demands. — The beating of 
the heart determines how much blood is sent out in a minute, 
but it does not determine what share shall be sent to each part 
of the body. That depends on the widening and narrowing 
of the small vessels in different regions. It is helpful to com¬ 
pare the changes in the distribution of the blood with those in 
the distribution of water in a town. Picture to yourself a 
busy village at ten o’clock in the morning. The water from 
the pumping station is probably forced up into a standpipe 
from which it runs out into the mains in the streets. At this 
hour of the day the liveliest flow is toward the downtown sec- 


CONTROL OF THE CIRCULATION 


119 


tion, the stores and the mills, because it is in these buildings 
that the most outlets are open. 

In the evening when these establishments have been left 
empty and dark, the water in their pipes will be more or less 
at a standstill. The same pressure as before is maintained at 
the standpipe, but now the principal movement of water is 
toward the homes of the people. In these houses the faucets 
are open in great numbers and toward them the supply stead¬ 
ily moves. If a fire breaks out in the business district, the 
situation will be quickly changed. As the hydrants are 
brought into use the main current shifts again toward these 
large openings, and it may be necessary to speed up the 
pumps to keep the pressure from falling. 

How do these conditions compare with those which may 
be discovered in the living body? Let us think first of the 
effect on the body of exposure to heat and cold. When the 
skin is warmed, it becomes flushed and this means that the 
blood vessels have become enlarged. A larger blood flow 
than before is now going on close to the surface. It is nat¬ 
ural to suppose that less blood than before is passing through 
the internal organs. We rely upon a hot bath to take blood 
from within and to give some relief in cases of headache, 
cold, and indigestion. On the other hand, when the skin is 
cooled, if the chilling is not too severe, it turns pale, which is 
a sign that its vessels have been contracted and that the blood 
must have been sent into the deeper tissues. These changes 
in the share of the blood flowing near the surface and that 
sent through the internal organs will be seen not to depend 
to any great extent on the action of the heart; what regulates 
them is mainly the condition of the muscular walls of the 
living blood vessels. 


120 


PHYSIOLOGY AND HEALTH 


When exercise is taken, adjustments must be made both in 
the heart and in the vessels. The arteries of the muscles open 
widely and myriads of capillaries which before were flattened 
and empty begin to convey blood. There is at the same time 
an increase of blood in the skin for the purpose of getting rid 
of the extra heat which is being produced. In the digestive 
organs there is an opposite change, a narrowing of the ves¬ 
sels, with the result that less blood finds its way through this 
region and more is available to supply the parts that need it 
urgently. Exercise is like the serious fire we have men¬ 
tioned. It is necessary to drive the pumping engine, in this 
case the heart, to meet the greatly increased demand. 

The brain, more than any other organ, needs to have a con¬ 
stant supply of blood. If this fails, the immediate result is 
fainting; if the circulation in the head should be arrested for 
more than a few minutes, the cells of the brain would be so 
badly injured that they could not be restored. Interesting 
experiments show that when the brain is being actively used, 
as in solving a problem, there is a tightening up of blood ves¬ 
sels in distant parts of the body, for instance in the arm. 
Such a contraction of arteries in various places improves the 
circulation in the brain where it is particularly needed. This 
is just what we wish to bring about when we are trying to re¬ 
store a victim of fainting. We place the head low so that the 
blood will go readily to it. Cold water applied to the skin of 
the face will cause a reflex contraction of a great many blood 
vessels there and the flow through the brain within will be 
assisted. Almost any sharp stimulus may be expected to have 
such an effect; that is why smelling of ammonia is helpful. 

Congestion. — This word means strictly ‘an increase of 
the blood in some part. 5 A distinction is made between active 


CONTROL OF THE CIRCULATION 


121 


and passive congestions. In the former the vessels are freely 
open and the blood is moving freely. In the latter the blood 
is meeting with resistance in getting through. The hand 
dipped in hot water illustrates active congestion, whereas a 
hand which is red (or blue) with cold illustrates passive con¬ 
gestion. The blood, as we say, has ‘settled’ in it. The cir¬ 
culation is evidently slow, for the veins are small and the dark 
color shows that the blood stays so long in the capillaries as to 
lose more of its oxygen than usual. 

Inflammation. — We use this term when we mean a dis¬ 
turbance in the condition of a part of the body which is 
more persistent and more abnormal than a simple congestion. 
When a region is irritated by a poison or by the activity of 
bacteria, an active congestion is likely to be the first effect. 
The region is flushed and hot. Then the vessels, especially 
the minute veins, show a tendency to become plugged, thus 
converting the active to a passive congestion. This plugging 
is probably due largely to the gathering of white blood cor¬ 
puscles in these passages. The flush deepens and becomes 
bluish; there is swelling as surplus fluid escapes from the 
capillaries; there may be throbbing and pain. If bacteria 
are present when such a state has developed, they may greatly 
increase in numbers in spite of the havoc wrought upon them 
by the white corpuscles. 

Inflammation at this point passes into suppuration (pus 
formation). With insufficient blood supply and the multipli¬ 
cation of bacteria, body cells die and disintegrate. These 
wrecks of cells, loaded with and surrounded by bacteria, 
living and dead, form the bulk of what is called pus , or 
‘matter.’ You may be inclined to think it is unfortunate that 
the circulation should be hindered in an inflamed spot. 


122 


PHYSIOLOGY AND HEALTH 


Perhaps it does injure the tissues at that place, but it helps to 
protect the rest of the body from a spread of the infection. 

The lymph. — We must bear in mind that most of the cells 
of the body are not actually bathed by the blood. It comes 
very near to them, but it is enclosed in the blood vessels which 
do not let it stray into the nooks and corners of the tissues. 
Between the capillaries and the cells there is usually a little 
space. There are spaces also between neighboring cells un¬ 
less they are uncommonly close together. All these minute 
spaces contain a fluid which is spoken of as lymph. It is 
held there much as water is held in a sponge. Lymph is seen 
when a blister is pricked; in this case two layers of the skin 
have been separated and the space formed between them has 
become filled with lymph. 

Lymph is much like the fluid part, or plasma, of the blood. 
The capillaries do not ordinarily let the red corpuscles escape 
from the blood, but the walls are so delicate that dissolved 
substances pass through them and come to be found in nearly 
equal amounts within and without the vessels. You will see 
that the cells actually feed on supplies furnished by the lymph. 
By doing so they reduce the quantity of such food materials 
in the lymph and would soon use them all if the blood did not 
promptly transfer fresh portions to make good the loss. In 
the same manner the cells absorb oxygen from the lymph and 
the passing blood renews the supply. The waste products of 
the cells would overload the lymph if it were not for the con¬ 
tinual removal of such products by the blood. The lymph 
is often said to be the middleman in the exchanges between 
the living tissues and the blood. 

The lymphatics. — So far we have spoken of the lymph as 
though it were quite stationary. But, as a matter of fact, 


CONTROL OF THE CIRCULATION 


123 


there is a system of vessels 
by means of which it can be 
drained from all parts of the 
body. These vessels are 
small and not easily seen. 
They resemble small veins 
and like them are made up 
by the union of still finer 
branches, the lymph capil¬ 
laries. New lymph is al¬ 
ways being formed and the 
lymph previously present is 
pushed along these channels. 
It is led to the chest where 
the largest of the lymphatics 
finally connects with the 
great veins close to the heart. 
Here the lymph merges with 
the blood. The movement of 
the lymph from the outlying 
regions of the system toward 
the chest is very gradual. 
If the large lymphatic in 
the chest is cut, the lymph 
does not stream from it as 
blood would from a vein 
of the same size; it merely 
drips. 

Why does lymph move at 
all ? The simplest answer to 
this question is already sugge 



DIAGRAM OF THE DRAINAGE 
SYSTEM FOR THE LYMPH 
i. Thoracic duct. 2. Right lym¬ 
phatic duct. 3. Left subclavian 
vein. 4. Right subclavian vein. 
5. Superior vena cava. 6. Lacteals. 
7. Lymphatic glands. The small 
tubes connecting with the lymph 
spaces in all parts of the body are 
the lymphatics. 

ted. As new lymph is formed, 











124 


PHYSIOLOGY AND HEALTH 


other lymph is crowded away and makes its escape along the 
lymphatic vessels. We may also consider that the fresh 
lymph is under a certain pressure. It has been filtered from 
the capillaries where the blood presses with considerable force 
upon the walls which confine it. The lymphatics in the chest 
open into veins in which there is scarcely any pressure. The 
lymph will naturally move from the higher toward the lower 
pressure; the principle is the same as with blood. Many of 
the lymphatics are provided with valves similar to those in the 
veins; when the muscles compress them, the lymph slips along 
toward the chest; when the muscle pressure relaxes, they re¬ 
fill from the outlying parts. 

When a cut in a finger becomes seriously infected with cer¬ 
tain kinds of bacteria, the trouble may spread along the course 
of the lymphatics through the tissues of the hand and up the 
arm. These lymph vessels may become visible as shining, 
wavy streaks under the tense and flushed skin. At the same 
time small tender kernels, or nodules, may be felt in front of 
the elbow and perhaps at the armpit. These are the struc¬ 
tures commonly called lymph glands. They seem to be sta¬ 
tions on the path of the lymph which hinder the march of in¬ 
fection toward the chest. When examined under the micro¬ 
scope, their appearance suggests that they are filters for the 
sluggish stream. 

We usually think of the lymph as a bearer of wastes from 
the living tissues, but in one case it has quite a different serv¬ 
ice. The lymph which originates in the wall of the small in¬ 
testine during digestion brings into the circulation some 
freshly absorbed food. When this process is going on, the 
lymphatics which lead from the intestine may appear like 
slender tubes filled with milk. The peculiar whiteness of 



CONTROL OF THE CIRCULATION 


125 

such lymph is really due to the same condition which makes 
milk white, the presence of tiny globules of fat. 

Discussion 

1. What happens to the circulation when one. blushes? 

2. Why is one drowsy after a heavy dinner? 

3. Discuss the amount of work done by the heart when one is 

lying and when one is standing. 

4. How is it that the nervous system can slow up or speed up the 

circulation? 

5. What is the value of elasticity of the walls of the blood 

vessels? 

6. Compare the distribution of blood to different parts of the 

body with the distribution of a city water supply. 

7. What is required of the circulation during exercise? 

8. Discuss congestion and inflammation and show how these 

processes protect other parts of the body. 

9. Discuss the nature of the lymph and the way in which it 

moves. 

Experiments 

1. Put the hand in very warm water for five seconds. Explain 

the changes in its appearance. Make a similar experi¬ 
ment with ice-cold water. Compare the appearance of the 
veins in the two instances. 

2. Take the pulse when lying down after you have been lying 

quietly for five minutes. Stand up and take the pulse 
again. What is the difference in the pulse rate? 

3. Let the arm hang by the side for a minute. Hold it straight 

over the head for a minute. Explain the difference in the 
appearance of the skin and the veins. 

4. Draw the finger along a vein in the skin of the arm. Ob¬ 

serve that the refilling takes place from the extremity. 
Keep watch for evidence of valves when the blood is pushed 
the wrong way in the vein. 


IX 


BREATHING 

Where in the body do blood and air meet? Is there still a wall 
between them? 

When blood takes on oxygen, what does it give up? 

How much air do the lungs of a man usually hold? Under what 
conditions can the amount be increased? 

Why should we breathe through the nostrils rather than the 
mouth? 

What are the properties of air in a badly ventilated room? 

What are the problems in breathing for the mountain climber 
and aviator? 

Would it benefit our bodies if under ordinary conditions we should 
breathe pure oxygen instead of air? 

You have learned that the blood is sent through the lungs 
to receive oxygen and to get rid of carbon dioxide, the chief 
waste product of all living cells. The blood and the air 
we breathe are brought into close contact. The tissue of the 
lungs is very light and spongy. In fact, the lungs of animals 
are often spoken of as ‘the lights.’ 

Air reaches the lungs by means of the trachea and bronchial 
tubes. The trachea is a large elastic tube which you can feel 
in front of your neck. Probably you call the larynx at the 
top of it the ‘Adam’s apple.’ The many passages formed by 
the division of the trachea are the bronchial tubes. When a 
lung is dissected, one can trace air passages in it which branch 
and become smaller and smaller, until they end in tiny, 

126 


BREATHING 


127 

elastic air sacs. There are many millions of these, and they 
are extremely small, smaller than the smallest bubbles in soap¬ 
suds. The microscope shows that each one of these minute 
air sacs is wrapped about by a network of capillaries. 

If you can imagine a structure like this you will under¬ 
stand that there are really two layers of cells between the 
blood and the air. One layer belongs to the air sac, the other 



AN AIR SAC 

This shows the thinness of the wall, the relation of the blood capillaries, 
and the air tube leading into it. 

makes the capillary wall. But these cells are of the thinnest 
and most delicate sort to be found anywhere in the body. 
The two layers probably let the gases pass to and fro as 
readily as they would pass through the film in a soap 
bubble. The blood is aired as thoroughly in the lungs as if it 
were sprayed into the air and then collected again. 

The amount of air in the lungs of a man may be something 
like three quarts. If he should hold his breath, it is plain 





128 


PHYSIOLOGY AND HEALTH 


that the nature of this air would change. Its oxygen would 
be reduced and its carbon dioxide would be increased. Very 
soon the blood leaving the lungs and passing on through the 
left side of the heart to the arteries of the body would not be 
up to its regular standard. When such imperfectly aired 



LUNGS AND AIR PASSAGES 

The right lung shows the lobes and their divisions, the lobules. The 
tissue of the left lung has been cut away to show the air tubes. 

blood reached the brain, it would produce a feeling of breath¬ 
lessness, and this would shortly make it impossible to con¬ 
tinue holding the breath. It is the quality of the blood sup¬ 
plied to the brain that determines how fast and how deeply 
we shall breathe. 

When we breathe, we do not empty the lungs entirely and 




BREATHING 


129 



BACK VIEW OF HEART AND LUNGS 



































130 


PHYSIOLOGY AND HEALTH 


then refill them with fresh air. We breathe out only a part 
of the three quarts just referred to and breathe in a similar 
amount of new air in its place. The quantity of air received 
or discharged in a quiet, easy breath is about a pint. Of 
course, when it is necessary, we can breathe much more deeply 
and also more rapidly. Even though in quiet breathing a 
single breath amounts to only a pint, we must remember that 
we breathe about sixteen times in a minute and thus two gal¬ 
lons of air pass in and out in this short time. When a large 
man is hard at work, he may breathe a great deal more than 
this, perhaps twenty gallons a minute. 

It would take too long to explain here just how the muscles 
enlarge the chest so that air may be drawn into the lungs. 
The diaphragm, the flat muscle which forms the floor of the 
chest cavity, and the muscles which lift the ribs are all used 
in the process. Some persons have the idea that the lungs 
swell and force out the chest, but the lungs themselves 
have no power to move; they follow the changes in the 
size of the chest. When we raise our ribs, the chest cavity 
enlarges and the lungs stretch out to fill it. This causes their 
millions of air sacs to become larger and the air crowds in to 
fill them. When the ribs return to their first position, the 
chest cavity becomes smaller and some air has to be forced 
out of the lungs. 

The breath usually comes and goes by way of the nostrils. 
There are two or three reasons why it is better to have it pass 
through them than through the mouth. The spaces in the 
nose are much divided by partitions with curled surfaces, 
covered by a moist membrane well supplied with blood. 
As the passing air moves over these surfaces, it is 
warmed and water is taken up by it. If cold and dry air is 


BREATHING 


131 

drawn directly through the open mouth, it has both a chilling 
and a drying effect on the lining of the throat. The nose also 
filters the air. The dust particles which are often so numer¬ 
ous in the air are caught by the membranes. It may seem 
disagreeable to think of this dirt as settling on this surface, 
but it does not remain there long. It is moved toward either 
the nostrils or the throat by small waving processes (cilia) 
which project from each epithelial cell. It will be seen, there¬ 
fore, that the nose does three things to the air passing through 
it on its way to the lungs: it warms it, 
moistens it, and frees it almost com¬ 
pletely of dust. Among the dust par¬ 
ticles there may be some germs which 
might cause disease. 

The air that we breathe out is warm 
and moist; it is also poorer in oxygen 
and richer in carbon dioxide than when 
we inhaled it. These last two changes have taken place in the 
lungs. There the blood has been affected in just the opposite 
way; it has become rich in oxygen and poor in carbon dioxide. 
We say that it has been changed from venous to arterial blood. 

The air is not altered as much as is commonly supposed in 
its journey through the lungs. When it comes out it still 
contains as much as four-fifths of its original oxygen. It 
would not be very unpleasant to breathe this air a second 
time, but a third use would doubtless be distressing. Of 
course we try to ventilate our rooms so thoroughly that very 
little of the air will be breathed more than once. 

Good and bad air. — We know that when a room is not well 
ventilated the air seems unpleasant. Those who breathe it 
get drowsy or uncomfortable. They may have headaches. 



CELLS FROM THE 
BREATHING PASSAGES 
SHOWING CILIA 


132 


PHYSIOLOGY AND HEALTH 


Just what is the matter with the air in such rooms? At one 
time it was thought that it was poor in oxygen, but now we 
know this is rarely true. Later it was supposed that the 
carbon dioxide might have increased so much as to be rather 
poisonous, but this is not at all likely to happen. The facts 
are that air in badly ventilated rooms is often moist, usually 
too warm, and often has a disagreeable odor. These quali¬ 
ties make it harmful and lead us to increase the supply of 
fresh air. Another thing to remember is that the air in poorly 
ventilated places is nearly stationary, or stagnant. We do 
not like strong drafts; yet we feel better when there are gentle 
currents of air fanning our bodies than when there are none. 
Experiments have shown that bad air affects our skin rather 
than our blood. 

The control of breathing. — We think of breathing and 
the beating of the heart as two activities which have to go on 
as long as we live. There is an important difference between 
the two. The heart beats because the power to do so is part 
of its own nature. It does not depend on signals or orders 
from the central nervous system. The muscles used in 
breathing, however, have no such special ability to work by 
themselves. Like any other muscles attached to the bones, 
they are paralyzed if their nerves are cut. Every breath is 
taken because impulses have been sent from a station in the 
nervous system to call these muscles into contraction. This 
station is called the respiratory center. It is a very definite 
spot in the lower part of the brain just above the opening 
through which the spinal cord leaves the base of the skull. 
The French investigators who discovered this center called it 
The vital knot’ — hardly too strong an expression, since its 
operation is absolutely necessary to life. 


BREATHING 


133 


In order to get oxygen to the tissues and to relieve them of 
carbon dioxide, the breathing and the circulation must co¬ 
operate. It is of no great value to speed up one and not the 
other. The problem of carrying oxygen to the cells which 
need it is like sending freight from one city to another by a 
route which has to make use of two railroads with a junction 
somewhere on the way. If the number of cars running on the 
first road is increased and nothing is done to add to the num¬ 
ber of cars on the second road, the freight will simply pile up 
at the junction. In the same way, increasing the amount of 
air breathed without moving the blood more rapidly on its 
course will not benefit the tissues. With certain diseases of 
the heart there is a feeling of breathlessness and a great effort 
to get more air, but the trouble cannot be relieved unless the 
heart can do its part. There is plenty of oxygen at the trans¬ 
fer point, the lungs, but poor service beyond. 

Carbon monoxide poisoning. — We read now and then 
about cases of poisoning by carbon monoxide. This is a gas 
which must not be confused with the carbon dioxide we have 
just been talking about. Carbon monoxide is found in il¬ 
luminating gas and also in the exhaust from automobiles. 
To breathe this gas even in small amounts is very dangerous. 
We can easily explain why it is so deadly. You have been 
told that hemoglobin, the red substance in blood, can unite 
with oxygen, carry it to the tissues, and there part with it. 
Now it happens that when hemoglobin has a chance to unite 
with carbon monoxide, it will do so rather than combine with 
oxygen. When this occurs, a useless compound is formed, 
and the power of the blood to carry oxygen is decreased just 
as truly as if the red corpuscles were taken out of it. If a 
man runs the engine of his motor car in a closed garage, he 


134 


PHYSIOLOGY AND HEALTH 



may be overcome by the carbon monoxide which he inhales. 
It is odorless, and hence the man has no warning. 

Breathing at high altitudes. — One of the conditions to 
which the body must often adapt itself is that of high altitude. 
The mountain climber and the aviator must somehow get 
enough oxygen from the thinner air which surrounds them at 


LIEUTENANT A. SOUCEK 

This aviator flew seven and a half miles into the air. Why was it 
necessary for him to breathe from an oxygen tank ? 

high levels. At the top of Pikes Peak the air is not much 
more than half as dense as at sea level. The blood will not 
take so much oxygen at such a height as it does in the low¬ 
lands. It will, however, absorb more than might be expected. 
Persons who go to this elevation are likely to be upset by the 
change. They may have what is called ‘mountain sickness’; 
at least they cannot be very active without extreme breath- 



BREATHING 


135 


lessness. In time, however, they can become accustomed to 
the situation, or ‘acclimated/ as we say. The number of 
their red blood corpuscles increases. Each corpuscle can 
take somewhat less oxygen on its journey through the lungs 
than it would capture from the denser air by the seaside; but 
if the number of corpuscles is made larger, the total supply 
of oxygen to the tissues will not be greatly reduced. The 
actual increase of red corpuscles may be as much as a quarter 
or a third of the original number. To reach exceptionally 
high altitudes, tanks from which oxygen can be inhaled must 
be used. Such tanks have made it possible for aviators to 
fly more than 30,000 feet above sea level. Of course, the 
extreme cold is an additional hardship. 

There is a difference, which ought to be understood, be¬ 
tween the want of oxygen at great heights and the difficulty 
of a man whose breathing is interfered with in more common 
ways, as by choking. When the breathing is prevented, car¬ 
bon dioxide gathers in the body and that has a more disturb¬ 
ing effect than the lack of oxygen which develops at the same 
time. The aviator has no trouble in ridding himself of car¬ 
bon dioxide; it is only the want of oxygen from which he 
suffers. 

Breathing pure oxygen. — It is sometimes said that 
breathing pure oxygen is stimulating. That is what you 
might expect if you have seen how brightly a match burns in 
this gas. But really, if a man is given pure oxygen to breathe 
from a tank, he does not find himself excited. He feels just 
as he did before. It must be remembered that the cells of the 
body generally have more oxygen offered to them than they 
need and that they allow a great deal of it to pass by, through 
the capillaries, into the venous blood. If the blood comes to 


PHYSIOLOGY AND HEALTH 


136 

them with still more oxygen, they will still take only what they 
require and let the rest go unused. 

There are conditions, however, when breathing oxygen has 
some effect. In pneumonia, for instance, when parts of the 
lungs are useless and the heart is not working well, it may be 
helpful to let the patient inhale extra oxygen. The gas may 
be blown into a little tent which is set up over his face. In 
this case oxygen is not being brought in good measure to the 
tissues, and the supply can be made more nearly sufficient by 
forcing as much as possible into the blood. It is also some¬ 
what beneficial to an athlete to get a few deep breaths of oxy¬ 
gen before he starts on a short run. He will not necessarily 
break his record, but he will stand a better chance of equalling 
it and he will finish with less discomfort. In a short dash he 
is about to call for all the oxygen which can possibly be col¬ 
lected and the extra storage in his lungs and blood has a cer¬ 
tain value. 

Deep breathing. — It is a fine thing to cultivate the power 
to breathe deeply, but it is not possible to breathe deeply all 
the time. If the experiment is carried on too long, one be¬ 
comes dizzy or faint. We alter the make-up of the blood 
and begin to be affected by the change if we breathe a good 
deal more air than we need. 1 Our nervous system op¬ 
erates in such a way that we naturally breathe neither too 
much nor too little, though a few deep breaths now and then 
have a rather refreshing effect. Deep breathing exercises, 
if they are not overdone, help to give good posture. They 
also help to keep the tissues of the lungs in a healthy state. 
If deep breathing is not occasionally practised, there may be 

1 Probably because we then lose too much carbon dioxide from the blood. 
A certain amount of this gas in the blood is necessary. 


BREATHING 


x 37 


parts of the lungs in which the air is hardly changed at all. 
The circulation in these parts will also be poor, and it is 
thought that tuberculosis is more likely to begin in disused 
regions of the lungs than in others. 

The best breathing exercises are probably those which are 
taken without any special intention, as a part of other activi¬ 
ties. You cannot run, play tennis, or take any other vigorous 
exercise without training the breathing muscles which en¬ 
large the chest cavity and stretch the lungs at the same time. 
Another useful exercise is singing. Students usually sing in 
the schools, but older people do not sing enough. Besides 
the pleasure we get in singing, it develops the ability to ac¬ 
commodate a great deal of air in the chest and then to con¬ 
trol the manner of breathing it out. 

The voice. — The healthful and proper use of the voice is 
closely related to the manner of breathing. Tones are pro¬ 
duced by the vocal cords, which are stretched across the voice 
box much like the lips of a cornet player across the mouth¬ 
piece of the cornet. When air passes through the voice box, 
the vocal cords vibrate, and the tone which is produced de¬ 
pends upon the position or condition of the cords. If these 
cords are stretched tightly, the tone is high. If they are held 
more loosely, the tone is lower. The passages of the mouth 
and nose form the resonating, or resounding, chamber of the 
voice in much the same way as the tubes of the cornet form 
the resounding chamber for that instrument. The way in 
which this resounding chamber is used, together with the posi¬ 
tion of the tongue and teeth, determines the sounds we make 
in speaking and singing. 

You have doubtless noticed the different qualities of voices 
in different persons. Some have a voice which is clear and 


PHYSIOLOGY AND HEALTH 


138 

pleasant; others talk with hard rasping sounds. It is much 
pleasanter to listen to the conversation of a person who has 
developed proper use of the voice. The speaking voice ought 
to be more like the singing voice in the quality of its tone. 

If the control of breathing and the position of the chest and 
head are correct, better tones will result. The chest should 
be well filled during speech, and the pushing of the breath 
through the voice box should come from the action of the 
diaphragm. The main muscles of the throat should be re¬ 
laxed. 

Many persons develop an unpleasant voice because they 
let the head hang forward and talk with the lungs only partly 
filled. The muscles of the throat try to do all the work. The 
resulting tone is poor; the voice soon becomes tired and will 
not carry for long distances. If you lean forward with 
your elbows close together on your desk, your chest will be 
contracted and your speaking tones will be poor. Contrast 
this with the tone you get when you assume the right position 
and start singing or when you shout at some one across the 
street. This will give you a good illustration of the advan¬ 
tage of proper position and the unhampered movement of air 
in speaking. 


Discussion 

1. Describe the air sacs and the way oxygen gets into the blood. 

2. What muscles are used in breathing? 

3. Trace the path of the breath. 

4. Contrast the changes which take place in the red blood 

corpuscles while they are in the capillaries of the lungs 
with the changes which take place while they are in the 
capillaries of the body. 


BREATHING 


139 


5. What kind of air is found in good ventilation? 

6. How is the amount of breathing controlled? 

7. How does carbon monoxide poison the body? 

8. What is the effect upon breathing when one is several thou¬ 

sand feet above sea level? 

9. What would happen if you breathed pure oxygen? 

10. Under what conditions is it useful to breathe pure oxygen? 

11. What is the value of deep breathing? What is the best way 

to secure deep breathing? 

12. Discuss the health practices listed in the appendix which are 

related to this chapter. 

Experiments 

1. Measure the girth of your chest when you have breathed in 

and when you have breathed out: (a) during normal 
breathing; (b) during a deep breathing exercise. Repeat 
these measurements six weeks later. 

2. Test your outgoing breath for carbon dioxide by exhaling a 

few times into a test tube partly filled with lime water and 
then shaking the contents. (Carbon dioxide turns lime 
water milky white). 

3. Demonstrate a breathing exercise used in teaching singing. 

Discuss its value. 

4. Keep a record of the activities from which you get practice in 

deep breathing. 


X 


FOOD AND DIGESTION 

From what sources do the different types of food come? 

Just what is the process of digestion? 

What happens to food in the mouth? 

What are the parts of the digestive tract and what is the work 
of each? 

The uses of food. — All parts of the living body must have 
come at some time from the food. If a baby a day old 
weighs seven pounds and the same baby six months later 
weighs fourteen pounds, we must suppose that the added sub¬ 
stance has all come from the milk which the child has re¬ 
ceived. So it is natural when we think about food to regard 
it first of all as something from which new living tissues can 
be made. No doubt this is the most wonderful truth about 
the food of men and animals, but there are other uses which 
must not be forgotten. We still have to go on eating after 
we have stopped growing. What is the service of food in 
later life? 

Living matter is always wasting away. Food, then, has to 
be furnished to correspond with this wasting and to keep the 
body in repair. However, a much larger part of what we 
eat has a different use. It is to be oxidized, or burned, so that 
work may be done by the muscles and heat set free to keep 
the system warm. Most food serves as fuel. 

Quantities of fuel may be stored in the body for a long time 


140 


FOOD AND DIGESTION 


141 

before being used, just as in a power house fuel may be 
stored in coal sheds. In human beings the storage is chiefly 
in the form of fat. 

Kinds of food. — Water is a food which is not a fuel. It 
may be classed with building material because we cannot add 
new tissue unless water is furnished to become part of it. 
Most of the water which we drink is useful not as a building 
material, but as a carrier of other foods, which it dissolves 
and takes to the tissues of the body. It is also a carrier of 
dissolved waste products which it removes. Water is also 
needed to cool the body. This it does when it evaporates as 
sweat from the skin and moisture in the breath. More will 
be said about this peculiar use of water at another time. We 
take in a great deal more water than we do of any other food 
substance. 

Next to water the materials we eat most freely are the com¬ 
pounds which we call the carbohydrates. Cane sugar is one 
of these. There are other sugars in our food which most 
people do not think much about. There is one kind in milk 
which is not very sweet. Other kinds are found in fruits. 
We take even more carbohydrate in the form of starches. 
They are not sweet at all. Bread and potatoes contain starch 
in large quantities. The starches are foods which 
have to be ‘digested,’ as we say, before they can become 
useful to us. This means that they are not ready to become 
part of the blood and be offered to the cells of the body. They 
are almost impossible to dissolve unless they are first changed 
into other sorts of carbohydrates — in fact, into sugars. It 
is therefore true that a very important part of the action going 
on in the digestive organs is the changing of starch into sugar. 
The saliva can make this change. It will be found, for ex- 


142 


PHYSIOLOGY AND HEALTH 


ample, that a crumb of bread or cracker will come to have a 
rather sweet taste if it is kept for a while in the mouth. Some 
one has said that this is a simple way of making bread into 
cake. 

All the starch and sugar which we eat will be present in the 
blood at some later time as sugar. This sugar is the favorite 
fuel of the body cells, and a great share of it certainly goes to 
the support of the muscles as they do their work. There is 
only a very little sugar in the blood at any one time, but this 
amount is rarely reduced. If it is decidedly lessened, the per¬ 
son is disabled. This may happen to runners in the course 
of such long races as the Marathon. The carbohydrates of 
the diet come mostly from the plants. Probably the most 
important exception is milk sugar. 

The fats which we eat are secured largely from the animal 
kingdom. We get them in fat meat, cream, butter, egg yolk, 
and in various oils (like olive oil and cottonseed oil) which are 
obtained from the vegetable world. Fats are in many ways 
different from carbohydrates; they are liquids, or at least easy 
to melt; they will not mix with water; they burn furiously 
when actually set on fire, and there is no doubt that they make 
a similar contribution of energy to the body when they are 
burned in its cells. 

Our food has to supply us with still another class of sub¬ 
stances, the proteins. These are in many ways the most re¬ 
markable compounds in the world. We find them especially 
in those foods which were most truly living matter a short 
time before they were selected for eating. Lean meat, for 
example, which was active muscle, is largely made of proteins. 
An egg contains proteins in rather large amounts; not much 
of the egg is alive when it is first laid, but the protein there 


FOOD AND DIGESTION 


143 


will go to build up the cells of the body of the chick if one is 
developed. We must have protein for the growth and repair 
of our muscles and glands. Most vegetable foods contain 
less protein than is found in the same weight of meat or fish, 
but it is not hard to get as much protein as necessary without 
eating animal products. 

Protein and protoplasm sound somewhat alike, but they 
do not mean quite the same thing. Protoplasm is living mat¬ 
ter as it exists in cells. When such cells have been killed and 
are used for food, they will furnish the compounds which we 
call proteins. These must have been in the living proto¬ 
plasm, but they were probably associated there with other 
matter, such as water and mineral salts, and these are just as 
truly necessary to life as the proteins. 

You may be struck by the fact that the body is largely built 
from protein but is afterwards largely operated by making use 
of carbohydrates and fats. As a matter of fact protein can 
be employed for fuel, and much of it is constantly being ex¬ 
pended in this way, because we eat much more than is strictly 
necessary for the processes of growth and repair. 

Carbohydrates, fats, and proteins make up, with water, 
nearly the whole bulk of our ration. An active man may eat 
a pound of carbohydrate, a quarter of a pound of fat, and 
about a quarter of a pound of protein in a day. There are 
always other kinds of material, including mineral salts, mixed 
with these. If there were not, we should miss the great 
variety of flavor in our food. The tastes and odors that we 
enjoy are due to the presence of many compounds besides the 
three mentioned. Within a few years it has been shown that 
there are some substances absolutely necessary to preserve 
health which must be in any satisfactory diet, although the 


144 


PHYSIOLOGY AND HEALTH 


amount called for is very small. These are the vitamins, 
which you hear so much about today. 

The organs of digestion. — The digestive system is a mus¬ 
cular tube about twenty-five feet long. This great length is 
made possible because the intestine is so much coiled. Be¬ 
ginning at the mouth, the parts in order are: the pharnyx 
(throat), the esophagus (or gullet), the stomach, the small 
intestine, the large intestine (or colon). The stomach is the 
widest part of the system, and the small intestine is the long¬ 
est and in many ways the most important. In addition to 
these organs are the glands which send their secretions or 
juices into the canal and work upon the food to fit it for 
absorption. These are: the salivary glands (three pairs), 
which discharge saliva into the mouth; the microscopic 
glands in the lining of the stomach, which secrete the gastric 
juice in much the same manner as sweat is secreted through 
the pores of the skin; glands in the intestinal lining, which 
are somewhat similar to those of the stomach; the liver, which 
produces bile; and the pancreas. The last two empty into 
the small intestine just below the stomach. 

Voluntary muscles produce the movements of the jaw and 
tongue. They depend on their motor nerves to bring them 
signals from the brain and set them to work. The same is 
true of the upper part of the esophagus, but about halfway 
down the chest a different type of muscle begins to be found. 
This is slower in its movement and not so dependent on the 
central nervous system. The whole canal from this point 
onward is provided with this more sluggish and automatic 
form of muscle which is often called involuntary. It can 
carry out its usual movements fairly well even if it is not con¬ 
nected with the brain and spinal cord. 


FOOD AND DIGESTION 


145 



THE DIGESTIVE SYSTEM 








PHYSIOLOGY AND HEALTH 


146 

Food taken into the mouth is chewed — or should be — 
and at the same time saliva is poured in to mix with it. The 
muscles which bring the teeth together are very strong. 
Chewing food may mean treating it as harshly as though one 
stepped on it with all his weight. Of course very much less 
force than this will usually be quite enough. Well-chewed 
food will be broken into very small particles or shreds and 
mixed with almost its own volume of saliva. 

In the throat the path of the food crosses that of the breath. 
When food is swallowed, breathing must be interrupted. A 
muscular flap known as the soft palate swings back and blocks 
the way to the nose. The larynx is tucked under the over¬ 
hanging root of the tongue, and the food under pressure fol¬ 
lows the only way remaining open to it, which is down the 
esophagus. Swallowing is a reflex act; the food as it touches 
one spot after another causes nerve impulses to go to the brain, 
and the muscular contraction next in order is made to follow. 

The esophagus leads to the stomach by way of an opening 
in the great flat muscle called the diaphragm which makes 
the floor of the chest. The stomach is located higher up in 
the body than most persons suppose, and the larger part of it 
is to the left of the middle line. It is a muscular bag which 
can hold a quart or more, but which can at times be contracted 
to a much smaller size. When it is what we call ‘empty,’ it 
is slender and has deep creases running lengthwise. It is then 
likely to contain some air and small quantities of digestive 
fluids. 

The small intestine leads away from the lower and right- 
hand end of the stomach. The tapering part of the stomach 
which is next to the outlet is its most muscular and active 
region. When food is present, a series of wavelike move- 


FOOD AND DIGESTION 


147 


merits can be seen passing over this section. The contents 
are pushed toward the intestine, but often the opening is 
tightly contracted, so that the pressure results in a gentle 
churning. Meanwhile the main body of the stomach appears 
nearly motionless. It is keeping up a steady, moderate pres¬ 
sure on the food within. The opening to the esophagus is 
usually closed, relaxing for a moment after each swallow. 

The work of the stomach. — The chief service of the stom¬ 
ach in man is to make it possible for a full meal to be accom¬ 
modated. Those who have lost part of the stomach by sur¬ 
gery find that they have to eat little and often. Normally the 
stomach accepts a large quantity of food and then passes it 
little by little to the intestine. It has been compared to the 
hopper which takes in a sackful of grain and then lets it 
trickle down between the millstones. Besides acting as a 
reservoir for food, the stomach is a place in which some diges¬ 
tive changes take place. 

While, as you know, the saliva can turn starch into sugar 
of a certain kind, the food is not kept long enough in the mouth 
for this change to be completed. It continues for a time in 
the stomach. Cooked starch is quite readily made to un¬ 
dergo this change, but with raw starch the process is slow. 
Most of the starch in our food has been cooked, and the effect 
of the saliva upon it is remarkably rapid. Sooner or later 
this sort of starch digestion is stopped, because saliva is un¬ 
able to continue its work in an acid mixture and the gastric 
juice which gradually mixes with the contents of the stomach 
is decidedly acid. 

The gastric juice is likely to flow even before food arrives. 
It is started by the influence of nerve impulses from the brain, 
which are sent to the stomach when food is first tasted or even 


PHYSIOLOGY AND HEALTH 


148 

when it is anticipated. The stomach, as well as the mouth, 
waters at the sight of food. Once started, the gastric se¬ 
cretion continues as long as there is food in the stomach. The 
juice is a clear liquid, like water, and the most noticeable thing 
about it is the acidity which has just been mentioned. The 
acid in the juice as it comes from the glands is hydrochloric. 



GLANDS 

This diagram shows the principle of gland structure and the relation of 
blood capillaries to the gland cells. 

It probably has a very helpful influence in restraining fer¬ 
mentation or spoiling of the food and in destroying many 
germs of possible disease. 

Gastric juice puts an end to the digestive power of saliva 
and does not itself carry on the change of starch to sugar. It 
begins the digestion of another class of foods, the proteins. 
There is an agent, pepsin, in the juice which does this. The 
proteins in our food are partly dissolved and partly in solid 




FOOD AND DIGESTION 


149 


form. In either case they need to be modified; that is to say, 
even if a protein is in solution, like raw white of egg, it does 
not follow that it can be introduced directly into the blood 
and made to nourish the cells of the body. In fact, if white 
of egg is added directly to the blood, it is removed by the 
kidneys. Of course it is plain that solidified proteins, like 
boiled white of egg, must be dissolved before they can leave 
the intestine and enter the circulation. 

During the time that food stays in the stomach, the pro- 



INVOLUNTARY OR UNSTRIPED MUSCLE CELLS 

These are muscle cells found in the walls of the stomach and intestines 
as they appear when separated and seen through a microscope. 

teins are partially prepared to become acceptable food for 
the tissues, but a great deal of additional change is likely to 
be necessary in the intestine. Gastric juice has one curious 
property: it curdles milk. This has been known for ages, 
and extracts of the calf’s stomach have been used to make 
cheese. It seems odd that milk should be turned into a solid 
which has then to be dissolved again before it can be ab¬ 
sorbed. We generally expect just the opposite effect from a 
digestive juice. Probably the curdling of milk guards against 
the possibility that it will be passed on too rapidly to the 
intestine. 





150 PHYSIOLOGY AND HEALTH 

The work of the small intestine. — In small quantities, by 
a series of small ‘swallows/ food is transferred from the 
stomach to the adjoining intestine. The winding passage 
which must be followed from the outlet of the stomach to the 
beginning of the large intestine is about twenty feet in length, 
and it takes about four hours for a portion of the contents to 
cover this distance. This means an average progress of some¬ 
thing like an inch in a minute. The food does not steadily 
advance at this rate, but sometimes moves rather rapidly and 

then has a period of 
rest. When there is 
motion, it is due to the 
contraction of the tube 
just above a collection 
of food, which slides 
along under the pres¬ 
sure. You could work 
a glass bead through 
a rubber tube by pinching behind it with your thumb and 
finger again and again. What happens in the intestine is 
much like this, only it is not jerky. This movement is called 
peristalsis. 

About the time food begins to be pressed out of the stom¬ 
ach, very soon after a meal, the pancreas, that long slender 
gland lying under the stomach, «begins to secrete a valuable 
juice. This fluid flows through a duct into the upper part of 
the small intestine. At the same point the bile enters. This 
secretion is prepared by the cells of the liver. Its formation 
never ceases, but goes on more rapidly during the period of 
intestinal digestion. The duct connecting the liver with the 
small intestine has a short side branch which leads to a pear- 



DIAGRAM OF THE GLANDS, THE VILLI, 
IN THE LINING OF THE SMALL 
INTESTINES 




FOOD AND DIGESTION 


I 5 i 

shaped sac, the gall bladder. The bile from the liver may 
either pass directly to the canal or it may be turned aside and 
stored for a time in this container. Now and then the gall 
bladder may discharge a good deal of bile at once. The bile 
in the human body amounts to something like a pint in a 
day. It is very bitter, and its color varies from green to 
orange. A part of the matter dissolved in the bile is known 
to be waste, but there is something else present which favors 
the progress of digestion. Bile alone has very little power 



A COMPLETE VILLUS SHOWN IN CROSS-SECTION 


to digest foods, but it seems to help the pancreatic juice to do 
this. 

The change of starch into sugar which was interrupted in 
the stomach now continues. Proteins are further prepared 
for absorption, and fats begin to be made into other com¬ 
pounds suitable for admission to the circulation. In a healthy 
man whose diet has been well chosen, food is almost com¬ 
pletely digested; little that could be useful to the body is 
allowed to escape. 

The valuable products of digestion are largely removed 
from the interior of the small intestine to the circulation. 
This is the process of absorption. It is made more successful 
by the great extent of the surface with which the food is in 
contact. The lining is not smooth but greatly folded. Un- 















152 


PHYSIOLOGY AND HEALTH 


der the microscope it shows another peculiarity. It is found 
to be formed in a fashion which suggests velvet; that is, 
innumerable projections rise from it, making a sort of nap. 
These tiny pillars are called the villi. They have been 


PARTS 

OF 

DIGESTIVE 

TUBE 

MECHANI¬ 
CAL PRO¬ 
CESSES 

GLANDS 

LIQUIDS 

CHEMICAL 

CHANGE 

ABSORPTION 

Material 

By 

Mouth 

Cutting 

and 

Grinding 

Salivary 

Saliva 

Starch 

to 

Sugar 



Pharynx 

Raising Soft 
Palate 

Depressing 

Epiglottis 






Gullet 

Food Carried 
to Stomach 

Mucous 

Mucus 




Stomach 

Churning 

and 

Mixing 

Gastric 

Gastric 

Juice 

Proteid 

to 

Peptone 

Water 

Salts 

Sugars 

Peptones 


Blood 

Capillaries 

Small 

Intestine] 

Mixing 

and 

Moving 

Food 

Liver 

Pancreas 

Intestinal 

Bile 

Pancreatic 

Juice 

Intestinal 

Juice 

Starch to Sugar 
Proteid to Peptone 
„ f Emulsified 

a S l Decomposed 

Water 

Salts 

Sugar 

Peptone 

Fats 


Blood 

Capillaries 

Lacteals 

Large 

Intestine 

Food 
Forced on 

Mucous 

Mucus 


Water 



A TABLE OE DIGESTION AND ABSORPTION 


likened to the bristles of a flat brush, though this comparison 
gives the impression of something much too coarse. Each 
villus is covered with epithelial cells and has within it slender 
and winding vessels through which blood is flowing. 






































FOOD AND DIGESTION 


153 


The large intestines. — Not much digestion goes on in the 
large intestine because the processes have been so nearly com¬ 
pleted before it is reached. However, there is one important 
change brought about here: water is absorbed from the con¬ 
tents and the material which remains is much reduced in bulk 
and made comparatively solid. 

Constipation. — The rate of progress of the contents of the 
intestine varies a great deal in different persons and at differ¬ 
ent times. It is unfortunate when there is a long delay in the 
large intestine. Matter kept for more than a few hours in 
this part of the canal is more and more decomposed by the 
activity of bacteria. Some compounds may be produced 
which are poisonous to the system. Most writers now say 
that these poisons are not very injurious, for the intestine is 
slow to absorb such poisons and the tissues seem able to 
counteract them in most cases. Nevertheless the presence 
of any large amount of stationary material far down the in¬ 
testine appears to produce ill feelings: drowsiness, listlessness, 
and perhaps headache. Such conditions may not be so dan¬ 
gerous as is sometimes claimed, but they are certainly dis¬ 
turbing. 

The intestine can usually be trained to clear itself thor¬ 
oughly without requiring medicines. Drinking plenty of 
water is helpful and so is muscular exercise unless it is ex¬ 
tremely fatiguing. A generous quantity of roughage — 
coarser foods like fruits, vegetables, and bran — is beneficial. 
It is also important to have a set time for the movement and 
not to let anything interfere with it. 


PHYSIOLOGY AND HEALTH 


154 


1 . 

2 . 

3. 

4. 

5. 

6 . 

7. 

8 . 

9. 

10 . 

11 . 

12 . 

13. 


Discussion 

Name the two uses of food. 

Of what value is water to the body? 

Under what class of foods do we include starches and 
sugars? 

From what foods do we obtain these? 

Name the two other kinds of food material. 

In what foods is each found? 

What is the chief use of fats and carbohydrates? 

What can proteins accomplish which carbohydrates and 
fats cannot? 

What other substances are important in the diet? 

Make a list of the organs of the digestive tract in order. 

In which of these organs are carbohydrates acted on? Pro¬ 
teins? Fats? 

Name the juices which help digestion, and tell whence each 
juice comes. 

See if you can complete the following table: 


Class of Food 


Use Where Found Where Acted on Juices Which Aid 


1 . Proteins Growth Lean meat Stomach and Gastric juice from 

Repair Fish small intestine walls of stomach 

Fuel Eggs Bile from liver 

Pancreatic juice 
from pancreas 
Intestinal juice 
from walls of 
small intestine 

2 . Carbohydrates 

3 . Fats 


14. Discuss the health practices related to food and eating (see 

appendix). 

15. Explain the steps in the process of swallowing. 


FOOD AND DIGESTION 


155 


Experiments 

1. Weigh an apple. Place it on a radiator for a few days. 

Weigh again. What has caused the apple to lose weight? 

2. Burn a small piecer of lean meat. What is the material re¬ 

maining? 

3. Pour a few drops of iodine on a common cracker. What 

happens? (Iodine turns starchy foods to a bluish color.) 

4. Hold a piece of unsweetened cracker in the mouth. Does 

it begin to taste sweet after a time? 

5. Peristalsis may be illustrated in principle by showing how a 

bead can be worked through a rubber tube by pinching 
behind it. 


XI 


THE SERVICE OF THE ABSORBED FOOD 

Where is food stored in the body? In what forms? 

What do the cells of the body do with sugar? 

What is the work of the kidney? 

What are internal secretions? 

How can you gain or lose weight? 

Stored fuel. — The blood which passes from the intestine 
to the liver carries a great part of the absorbed food. You 
will see that the income of food is high a few hours after a 
meal while later, as in the morning before breakfast, it must 
be very low. Hence, in order to meet the needs of the muscles 
and other organs, the body must store its supplies. The 
form of storage which people know most about is fat. Even 
thin persons have more fat than would be supposed, while 
some individuals carry many pounds. 

The fat in the body is enclosed in cells within which it 
appears under the microscope like drops of oil. Not all the 
fat in the body has come from fat in the food. Most of it 
has been made from starches and sugars. This would be a 
difficult undertaking for a chemist in his laboratory, but it 
seems to be an easy one for the living cells. A cow eats very 
little fat in its ordinary food, but day after day it produces 
in great quantity the butter fat of the milk, most of which is 
manufactured from starch in the food. 


156 


SERVICE OF THE ABSORBED FOOD 


157 


The body does not store much carbohydrate. It makes 
over this type of food into fat, which is more condensed and 
easier to carry. There may be a few ounces of carbohydrate 
in the human system, however, mostly in the form known as 
glycogen. This is not quite the same as vegetable starch, 
but in most respects it is very like it. Glycogen is stored in 
the cells of the liver (where it was first discovered) and to 
some extent in the muscles and other tissues. You may re¬ 
member that the liver has a chance to act upon all the blood 
returning from the digestive tract. When sugar is being 
absorbed, the liver apparently collects it and puts it in stor¬ 
age in the form of glycogen. Later, when the intestine is not 
furnishing sugar to the circulation, the glycogen of the liver 
turns back to sugar again and thus the blood sugar is kept at 
its most favorable level. The liver has been called ‘the 
carbohydrate bank’ of the body, meaning that it is a place 
to make deposits in time of plenty and a reserve to draw 
from when necessary. 

This action of the liver is not wholly different from the 
service which a potato gives to the plant of which it is a part. 
The sap of the potato plant contains some sugar. When the 
weather is good and the green leaves are flourishing, this sugar 
tends to increase. In the potato under the ground some of 
it is turned to starch and put in storage. If the potato is not 
dug for the food of man but left in the earth, its starch will be 
kept until the time comes for the process of sprouting and 
the development of a new plant. Then it will be turned back 
to sugar and transported in the sap to the growing stalks and 
leaves. 

Much of the protein which we eat and digest is made into 
sugar and so has the same use in the body as carbohydrate 


PHYSIOLOGY AND HEALTH 


158 

food. Carnivorous animals do not eat much carbohydrate, 
but they have sugar and glycogen in their tissues because they 
produce them from proteins. The Eskimos are carnivorous 
men; they can get almost nothing but animal foods in their 
usual surroundings, so that they eat several times as much 
protein as we do. A great part of it goes to make sugar. 

The burning of fuel. — When a candle is burned, the wax 
steadily disappears. It has united with oxygen from the air 
and now forms two compounds, carbon dioxide gas and water 
vapor. When coal is burned, these two compounds form the 
main part of the hot gases which go up the chimney. Sugar 
and fat burn in the living body just as truly as coal in the 
furnace, and the same two products result. In the chapter on 
breathing we have described the way in which carbon dioxide 
is removed through the lungs. The water which is formed by 
such processes of burning or oxidation may leave the system 
through the kidneys, the skin, or the linings of the breathing 
passages. Most of the water which goes out by these routes 
is merely water that was taken in as food and drink, but a part 
of it has been made in the living cells by the burning of food. 

Carbohydrates and fats are usually burned completely to 
carbon dioxide and water. Proteins, however, cannot be 
changed entirely into these simple products; other substances 
are also formed, and these substances are not gases. Since 
some of the end products of the breakdown of proteins are 
solids, they cannot be removed through the breath, but must 
be dissolved so that they can leave the body as watery wastes. 
The sweat is such a waste, but it contains only very small 
amounts of the wreckage of the proteins. Most material of 
this class is found in the urine (the secretion of the kidneys). 

If we think of sugar and fat as being completely burned up 


SERVICE OF THE ABSORBED FOOD 


159 


into gases (like the candle), we may think of the proteins as 
burning more like coal, which leaves ashes instead of passing 
entirely up the chimney. This is a rough comparison, but a 
useful one. A coal stove gives more trouble than a gas range 
because there are cinders to dispose of. So it is natural to 
think that the body has more of a task to perform when re¬ 
moving the waste products from proteins than from carbo¬ 
hydrate and fat. Proteins are commonly supposed to put a 
burden on the kidneys, but it is quite likely that these organs 
are more hardy and enduring than has been thought. It has 
never been shown that the Eskimos are particularly subject 
to kidney disease. 

The kidneys. — The kidneys are a pair of organs fixed 
close to the muscles of the back below the diaphragm and at 
the level of the lower ribs. Each is fed by a very large artery 
and returns its blood through a large vein. Much of the 
circulating blood normally goes through the kidneys. These 
glands separate from the blood a quantity of water in which 
there are found most of those products of protein decomposi¬ 
tion which have to leave the body as dissolved waste. Much 
of the salt leaving the system is also taken out of the blood by 
the kidneys. 

Each kidney has a long, slender duct, or outlet tube, for 
its secretion. This passage extends to the muscular con¬ 
tainer called the bladder which makes room for the urine from 
both kidneys until a considerable quantity has gathered, when 
it is discharged. Many conditions affect the amount of the 
kidney secretion. The most important one within our own 
control is the drinking of water. There is no doubt that it is 
healthful to drink freely; in fact, this practice is hardly ever 
overdone. You are told, however, that most of the water 


i6o 


PHYSIOLOGY AND HEALTH 


should be taken between meals rather than at the table. The 
chief reason for this advice is that when water is swallowed 
with food it may be used instead of saliva to wash the food 
down. This inclines one to hasty eating and carelessness in 
chewing. 

The use of sugar by the body cells. — Wherever there are 
living cells, some burning of food must be going on, but some 
tissues are much more actively engaged in this process than 
others. The muscles consume most of the food. Compara¬ 
tively little can be needed by the connective tissues. The 
activities of the cells, especially of the muscle fibers, must be 
mainly carried on at the expense of sugar. You must bear 
in mind that all the sugar which is eaten and all the starch, 
together with a large fraction of the protein, is finally offered 
to the organs in this form. Whether fats also are changed to 
sugar before being burned is not yet certain. 

In any case you will see that it must be a serious matter for 
the body to lose the power to burn, or oxidize, sugar. This 
loss is not uncommon; it is the chief thing which is wrong in 
cases of diabetes. This disease may be mild or severe. It is 
considered mild when the subject can use some sugar in the 
diet though not as much as a normal man. It may be so 
severe that practically no sugar can be burned. When the 
condition is as extreme as this, even fat disagrees with the 
patient and the outlook is bad. It has been known for about 
forty years that the trouble underlying diabetes is failure of 
the pancreas to perform one of its offices. 

You have heard of the pancreas as a digestive gland. It 
has another function; besides sending its juice into the small 
intestine, it adds something to the blood circulating through 
it. This contribution from the pancreas goes everywhere 


SERVICE OF THE ABSORBED FOOD 161 

through the body, as a drug might go. When it is present, 
the muscles can burn sugar; when it is absent they cannot. 
Lately it has been found possible to make extracts from the 
pancreas of the calf and sheep which can be used for the relief 
of diabetes. When these extracts are injected under the skin 
the patient is greatly benefited. For a time he can use sugar 
in the normal way, but he is not cured. The dose will have to 
be repeated again and again. The product of the pancreas 
which is used in treating diabetes is called insulin. 

Internal secretions. — It is important to understand the 
action of the pancreas in making possible the oxidation of 
sugar in the most distant parts of the body. We have come 
to realize in the last few years that small organs which were 
once supposed to have no distinct value may be definitely 
necessary to the welfare of the whole system and indeed to 
life itself. Every organ has a chance to add compounds to 
the blood. When we come across an example of such action, 
we say that the organ has an internal secretion. Insulin is, 
then, the internal secretion of the pancreas. Several other 
examples will be given in another place in the text. 

Gaining and losing weight. — When a man has stopped 
growing, he may keep nearly the same weight over long 
periods of time, even for years. Usually this seems to hap¬ 
pen without any careful planning or regulating of the diet. 
It is really wonderful that the appetite should lead to this re¬ 
sult. It is hard to eat less than one wants in order to lose 
weight. It is just as hard for most persons to eat more than 
they want in order to gain. There are many persons who 
do eat too much for their good and come to be overweight, 
especially if they are lazy, for an idle man will gain on an 
allowance which is not enough for a man taking exercise. 


162 


PHYSIOLOGY AND HEALTH 


It is not so simple a matter to gain and lose weight as might 
be thought. If a man tries to reduce by exercise, he is bound 
to use up part of his body stores in doing so, but at the same 
time he may get a sharper appetite than he has ever experi¬ 
enced before; then if he eats all he wants, his hard work may 
seem to be wasted. It is difficult for many persons to add 
weight when their physicians think it would be well for them 
to build up their bodies. In this case idleness may diminish 
the appetite and so the individual may fail to gain. 

It is interesting to learn what happens when no food is 
eaten. Some persons have fasted for forty or even fifty days, 
taking nothing but water. The suffering is said not to be 
very great. There is a loss of weight which is not far from a 
pound a day. After a day or two the small store of carbo¬ 
hydrate in the body does not count as a reserve and almost 
the whole of the demand for food is met by using up fat and 
protein within the body. The subject has become a carni¬ 
vorous animal — living upon himself. 

Voluntary fasting is not usually so exhausting and distress¬ 
ing as the starvation of explorers and others whose food has 
given out. The volunteer can be made as comfortable as 
possible, protected from exposure, and not obliged to perform 
hard work. The explorer has to bear all sorts of hardships 
and cannot spare himself. So his strength is likely to fail, 
and he may die after only a few days without food. 

Death from thirst comes much sooner than death from hun¬ 
ger. If there is sweating, either from external heat or in 
connection with muscular activity, the loss of water from the 
body is very rapid and the demand for more to fill its place 
becomes urgent. Intense suffering results. In a tropical 
climate the end may be a matter of only two or three days. 


SERVICE OF THE ABSORBED FOOD 


163 

Special needs of the body. — It must not be forgotten that 
the diet may sometimes seem to be entirely sufficient, yet 
prove not to be so because of some special lack. Perhaps 
lime is not present in proper amount, or there may be a lack of 
iron or iodine. These are examples of elements which we need 
only in minute quantities, but which we cannot do without. 
So it is with the substances which we have called the vitamins. 
Various disorders (scurvy, rickets, beriberi, and probably 
other troubles) result from the use of food combinations from 
which some particular compounds of the utmost value are 
absent. Milk and leafy vegetables supply the vitamins which 
we are in some danger of missing if we do not take these foods. 

Discussion 

1. In what forms is food stored? 

2. Account for the fact that little carbohydrate is stored by the 

body. 

3. What are the sources of the water eliminated by the body? 

4. How do the protein wastes leave the body? 

5. What is diabetes? What contribution has science made in 

the treatment of this disease? 

6. What are the difficulties met in gaining and losing weight? 

7. What happens in the body when one fasts? 

Experiments 

1. Heat dry starch in a test tube. Note the water vapor which 

forms on the inside of the glass. Where did it come from? 

Try the same experiment with sugar. 

2. Record the number of pupils in your class who gain weight 

each month. What are the things which most commonly 

cause gain or loss in weight? 

3. Weigh yourself before and after lunch. 


XII 


PARTICULAR FOODS 

Why is appetite not the best guide in deciding what to eat? 

Is it wise to eat only the foods we like? 

How much sugar does the average American eat in a year? 

Why are desserts served at the end of a meal? 

How does a happy meal time aid digestion? 

Appetite as a guide. — Sometimes we hear it said that ap¬ 
petite is the best guide in deciding what to eat, that this is the 
way the lower animals do, and that they get on very well. 
On the other hand, many writers tell us that we ought to be 
sure to eat certain things which we may not especially like. 
One of the best students of these matters has said: “You may 
eat what you like when you have eaten what you should.” 
This suggests that appetite is not entirely a safe indicator of 
what should be chosen. One reason for this is found in the 
fact that we have a great many more foods from which to 
select than our forefathers did. Most of these dishes have 
been prepared to please the senses of taste and smell rather 
than to supply the exact needs of the body. That is why we 
sometimes need advice from those who know just what is in 
the various kinds of food. 

Sugar. — You have read in this book that the most im¬ 
portant food taken by the cells from the circulating blood is a 
kind of sugar. You may have wondered why, if this is true, 
there is any danger of eating too much sugar. There are 

164 


PARTICULAR FOODS 


165 

several reasons. In the first place, the sugar in the blood is 
not cane sugar. Again, cane sugar is much sweeter than the 
other sugars found in the vegetable world. Children enjoy 
its sweetness so much that they like to eat freely of candy, 
frosted cake, and other foods in which there is a great deal of 
sugar. When they have had as much as they care for, they 
have no inclination to eat other kinds of food. For this rea¬ 
son sweet desserts are sensibly brought on at the end of a meal 
rather than at the beginning. Furthermore, we eat very 
large amounts of cane sugar nowadays; the average Ameri¬ 
can consumes more than a hundred pounds of it in a year. 
Finally, cane sugar dissolves very readily in water or in the 
saliva, and any substance which is so soluble can be irritating 
to the stomach. 

When you learned that most of the carbohydrate eaten by 
men is in the form of starch and that this is turned to a kind 
of sugar by the processes of digestion, you may have felt like 
asking why we do not eat sugar altogether and save the body 
this work of making it from starch. One reason ought now 
to be clear; starch is not soluble and so it does not upset the 
stomach. The sugar formed from it is produced little by 
little and never amounts to much at one time. The cells of 
the intestine probably remove it about as fast as it is made 
from starch. Some kinds of sugar ferment in the stomach 
and intestine. Acids are formed which may make trouble if 
they reach unusual quantities. (This change of sugar to acids 
is almost exactly what happens when milk sours, and in fact 
milk sours very rapidly in the stomach. This is a natural 
and harmless process due to the action of living cells, mostly 
bacteria.) Sugar which remains in the mouth may be fer¬ 
mented. The acid which results is injurious to the teeth. 


PHYSIOLOGY AND HEALTH 


166 

This is especially true when the sugar has been mixed with 
some sticky or greasy substance, such as chocolate, which 
clings to the teeth. If you think it over, you will probably 
agree that there are at least these three objections to unlimited 
candy: it dulls the appetite for other kinds of food which may 
be distinctly needed by the body, it may cause indigestion, 
and it is bad for the teeth. Many young people find, besides, 
that candy is bad for the complexion. 

Meat. — Most children will eat too much sugar if they are 
not checked. Many of them will also eat too much meat. 
They like the flavor and keep on eating for the enjoyment of 
it when the system is not in need of the food. Some writers 
have claimed that meat is decidedly harmful, that it decom¬ 
poses in the intestine and forms really poisonous products, 
that it makes hard work for the liver and kidneys, and also 
that the tempers and characters of those who eat it are injured. 
All this appears to be greatly exaggerated. Stefansson, the 
Arctic explorer, tells us that the Eskimos, who live on meat, 
are remarkable for kindness and generosity. The real 
trouble with meat is much the same as with candy: it is so 
attractive to many persons that they make it too large a frac¬ 
tion of their ration. It is allowed to crowd out other articles 
of food which ought to be taken. Eggs are much like meat; 
the reason we do not hear constant warnings against eggs as 
food is probably that they are not so tempting; people do 
not commonly eat them to excess. There is a distinct objec¬ 
tion to the eating of much meat in warm weather; meat, eggs, 
and all foods which are rich in protein may fairly be called 
‘heating,’ in the sense that they cause the tissues to carry on 
their processes of oxidation at an increased rate. When one 
is uncomfortably warm to begin with, one does not wish to 


PARTICULAR FOODS 


167 

make matters worse by causing extra heat to be set free in the 
body. Eating much protein at such a time is like opening the 
drafts of the furnace when the house is already too warm. 
But, just as clearly, meat and other protein foods must be 
helpful in enduring the cold of winter. 

Vegetables and fruit. — As there are foods, like cane sugar 
and meat, which are often eaten too freely, so there are some 
foods which are wholesome, but which many young persons 
avoid. It is well to eat S&lads and vegetables. Some of the 
vegetables certainly do have odors that are not appealing to 
every one, but there are others that do not. If you can eat 
corn, peas, beans, asparagus, lettuce, parsnips, carrots, beets, 
squash, and radishes, you may be excused from onions, cab¬ 
bage, cauliflower, and turnips. If you like any or all of these 
latter, it is fortunate. 

Almost everybody likes fruit. Apples and oranges and 
grapefruit ought to be eaten, and fresh berries in their season. 
Vegetables and fruit do not give us a great deal of fuel or 
building material, but they furnish some of the valuable sub¬ 
stances which it will not do to omit from the diet. Such foods 
are beneficial in another way. They contain a good deal of 
indigestible matter. You might think that this would be in¬ 
jurious, but a moderate amount of it seems to be healthful. 
It gives enough bulk to keep the contents of the intestines in 
motion and scours and cleanses them in a mild way. Ma¬ 
terial which will not dissolve in the fluids of the canal is some¬ 
times spoken of as ‘roughage,’ or ‘ballast,’ two names which 
give a clear idea of its usefulness. 

Sea food. — Some children dislike fish. This is rather a 
pity. Fish, as well as oysters, lobsters, clams, and scallops, 
can replace meat at many meals if only they can be eaten with 


168 


PHYSIOLOGY AND HEALTH 


pleasure. These sea foods are much like meat in their 
make-up. Some of them are rich in fat (salmon, mackerel, 
and sardines); some are poor in it (cod and haddock). Sea 
foods contain a trace of iodine, which is needed especially by 
growing boys and girls. 

Mental states and digestion. — After all, it is important 
that we should enjoy our food. The combinations may be 
carefully made to be sure that everything called for is sup¬ 
plied yet the use of the food still not be successful if there is 
unhappiness of any kind. Over and over again experience 
has shown that indigestion may be caused by grief or anger 
or even milder feelings of a disagreeable sort. You have 
been told in an earlier chapter that the gastric juice flows 
when one takes pleasure in eating. This secretion may en¬ 
tirely fail if one is troubled in any way, and the proper move¬ 
ments of the stomach may also fail to be performed at such a 
time. Many years ago Doctor Cannon watched the stomach 
of a cat by means of the X-ray. He found that when the 
animal became restless and showed signs of temper the con¬ 
tractions of the stomach were stopped and the organ appeared 
like a lifeless, motionless bag. If he petted the cat until she 
became resigned to her situation, the usual deep rings of con¬ 
traction again passed in regular succession toward the pylorus 
(the gate between the stomach and small intestine). We 
may safely conclude that our own stomachs are affected by 
whatever disturbs us. 

We need, then, to be happy at meal times. Most of the 
food ought to be such as we like. It is not necessary that all 
of it should be exactly to our liking, for we should try to ac¬ 
quire a taste for foods that are good for us. We ought to 
have pleasant conversation when we are at the table. This 


PARTICULAR FOODS 


169 

is the worst possible place for unfriendly arguments and an¬ 
noying criticism. The food should be served attractively 
and the room should be sunny and airy. These things count 
for a great deal more than was formerly realized. They are 
especially important for the welfare of those whose appetites 
are not good and who have to be tempted by carefully planned 
meals. 

Deficiency diseases. — You have heard something about 
the remarkable substances called vitamins. You know that 
a vitamin is something absolutely necessary to the health of 
the body, though the amount needed may be very small in¬ 
deed. It is something which the cells cannot make for them¬ 
selves; so it must be furnished by the food. Probably all the 
vitamins, of which at least five are known, are made by plants. 
We may get them directly as we eat vegetable food or they 
may be collected for us by the lower animals. 

Milk is rich in vitamins. The cow probably receives them 
in her food and concentrates them in this secretion. Green 
foods, such as lettuce, spinach, and the young tips of aspara¬ 
gus, are found to provide these precious compounds. Milk 
and greens are sometimes called protective foods because they 
can make up for a possible lack of vitamins in other articles 
of diet. The rice which is the main part of the food of the 
Chinese would not keep them in health if it were not supple¬ 
mented by green leaves. The poorest people in Italy are also 
dependent on greens, for there is something lacking in the 
corn meal which is their chief support. The Arabs eat mostly 
barley bread with dates and some meat, but the sour milk 
which they consume is something they could not do without. 
The Eskimos have what seems to be a very limited and mo¬ 
notonous diet, composed entirely of meat, but they eat liver 


170 


PHYSIOLOGY AND HEALTH 


and other internal organs rather than muscle alone, and this 
liver contains vitamins. 

Those who fail to get particular vitamins are subject to 
disorders which are often called deficiency diseases. One of 
these is scurvy. In earlier times explorers and sailors on long 
voyages often suffered and in many cases died from this 
scourge. They became greatly weakened; their mouths 
were sore and their teeth loosened; the bones became fragile; 
small blood vessels broke under the skin, and there were 
other symptoms. Something was lacking in the ration. 
Physicians knew that the need was for fresh food and greater 
variety. Experience showed that fruits helped to prevent 
or cure scurvy, and for many years in the British navy lemon 
or lime juice was supplied for this purpose, and British ships 
or sailors used to be called dime juicers’ for that reason. 

We now believe that scurvy is due to the want of a special 
substance which we call ‘Vitamin C.’ This one, more than 
the other vitamins, is likely to be destroyed by the heat used 
in cooking. Babies may suffer from a form of scurvy, espe¬ 
cially when the milk fed to them has been scalded or pasteur¬ 
ized. If they are given some orange juice, the missing vita¬ 
min is replaced in the food. Heating the milk helps to kill 
germs of disease; so it is fortunate that we can take this pre¬ 
caution and still have protection against scurvy. 

Another deficiency disease, and one which is far more com¬ 
mon than scurvy, is rickets. The chief feature of this dis¬ 
order is a poor development of the skeleton. The bones are 
not strong, but are easily bent by the weight of the body or the 
pull of muscles. In babies and little children this condition 
results in bowlegs and other deformities. At the same time 
the general health is poor. The strength of bone depends on 


PARTICULAR FOODS 


171 

the proper deposit in it of the salts of lime, especially the 
phosphate. To build bone, of course it is necessary to have 
these materials in the diet. But even when they are eaten, the 
body seems to need the assistance of some other substance, 
Vitamin D, to cause the development of a strong, well-pro¬ 
portioned skeleton. 

There is some strange relation between Vitamin D and 
sunlight. Rickets is much more likely to affect children in 
the winter months than in summer. When the sun does not 
climb high above the horizon, its rays reach us after a long, 
slantwise journey through our atmosphere and some of their 
strength is lost. Then, too, most of the light which does 
come to us arrives at last through window glass. The glass 
reduces the power of the light to bring about chemical changes. 
Children who are kept indoors are particularly likely to have 
rickets unless their food is well provided with the vitamin. 
Cod-liver oil has long been given to children threatened with 
rickets and has proved very beneficial. We now know that 
this oil is rich in Vitamin D. 

The codfish gets Vitamin D from the plant food upon 
which it feeds and stores it in its liver. Men catch the fish 
and make use of the oil from the liver for their own benefit. 
As we have said, the Eskimos include liver in their diet. In 
the Arctic zone the sun never rises high; for long periods it is 
not seen at all. These conditions would probably cause 
rickets in the children if their food did not protect them. 
There are several other diseases besides scurvy and rickets 
which appear to be due to defects in the food ration, but these 
two will answer to illustrate the principle. 

Long ago a New Englander named Sylvester Graham 
taught that it must be dangerous to health to refine our food 


172 


PHYSIOLOGY AND HEALTH 


to an extreme degree. When we do so, we must be in danger 
of discarding some material which we ought to receive. 
Graham flour, which preserves the name of this interesting 
writer, contains all the coarse husks of the grain as well as the 
fine white contents of the kernels. We can see in the teach¬ 
ing of Graham the germ of the vitamin idea: that we need not 
only proteins, fats, and carbohydrates to keep us well and 
strong, but also a number of other compounds which we are 
more likely to get if we choose a varied diet. 

Discussion 

1. Explain why the candy habit is not a desirable one. 

2. Why is starch a better fuel food than sugar? 

3. What should be the difference in the winter and summer 

diets? 

4. Why is an excess of protein undesirable? Which class of 

foods is most likely to be slighted? Why is this unwise? 

5. What is scurvy? Rickets? How may they be prevented? 

Experiments 

1. Put a small amount of sugar into a test tube partly filled with 

water. What happens to the sugar? Perform the same 
experiment with starch. What difference do you note? 
Does this help you to understand why starch is changed 
into sugar before being taken into the blood stream? 

2. Boil a small amount of starch. What change has taken 
place? 

Keep a record for a week of the fruit and vegetables you eat 
each day. 


3 . 


XIII 


INCOME AND OUTGO 

Could the efficiency of the human body be studied like that of 
an engine? 

How can one find out the amount of heat produced by the foods 
we eat when they are oxidized in the body? 

What difference should there be between the food requirements 
of a bookkeeper and those of a woodchopper? 

You have learned something about the different kinds of 
food. How much of each kind is likely to be taken in an 
ordinary day? Questions like this one have interested men 
of science for more than a hundred years. There are great 
laboratories in many cities where the study of food has been 
going on. Often in such places it is not only the diet which 
is examined, but also the persons who are receiving it. The 
income and the outgo of the body are both measured. In¬ 
come means food, drink, and oxygen. Outgo includes not 
only the waste from the kidneys and intestine, but also what 
is lost from the lungs and even from the skin. Changes in 
the weight of those who are experimented upon receive close 
attention. 

Engineers frequently make very similar studies of power 
plants. They learn all that they can about the nature of the 
coal; they weigh the amount shovelled into the furnaces 
while the test is going on; they examine samples of the gases 
which go up the chimney; they measure the horsepower, or 

173 


i 74 


PHYSIOLOGY AND HEALTH 


work done in the engines. All these figures they bring to¬ 
gether to discover how one influences another. 

Food quantities. — If such a trial is to be made with a hu¬ 
man being, the ration given to him may be selected by the 
investigator or it may be just what the consumer chooses for 
himself. When different persons are allowed to eat what 
they like and the portions served to them are noted, the fact 
appears that the diets do not vary so much as might be sup¬ 
posed. Different persons have very different tastes, but they 
usually consume about the same quantities of protein, fat, 
and carbohydrate. One man may like meat and get much of 
his protein in that food. Another may not be so fond of 
meat, but he may get an equal amount of protein in eggs, 
milk, peas, and beans. There is some variation in the pro¬ 
portion which may exist between carbohydrates and fats, but 
the former generally amount to several times the weight of 
the latter. Carbohydrates make the main mass in most diets. 

Those who study quantities of food and waste use a unit 
of weight called the gram. This is not familiar to us in our 
home life, but the metric system is much more convenient than 
the ounce or the pound for calculations and tables. A gram 
is a small weight; it takes about 28 of them to make an ounce 
and about 453 to make a pound. A five-cent piece weighs 
about 5 grams. 

A man may be found to eat 75 or 100 grams of protein in 
24 hours. The fat in his ration may be about equal to the 
protein. The carbohydrate is likely to run to 300 or 400 
grams. Of course, the food and drink of the day will have 
furnished him in addition a great deal of water, perhaps 2500 
grams. These are figures for a day in which little exercise is 
taken. With hard work during long hours all the figures 


INCOME AND OUTGO 


1 75 

might be larger, with the greatest increase for carbohydrate 
and least increase for protein. 

Waste products. — The two principal waste products, as 
you know, are carbon dioxide gas and water. The quantity 
of carbon dioxide is surprisingly large. Often it is more than 
100 gallons a day, enough of the pure gas to fill a balloon more 
than 3 feet in diameter. Of course, the air which we breathe 
out is not pure carbon dioxide, but only a three or four per 
cent mixture of it with the other gases. Almost all the carbon 
dioxide leaving the body has been formed within it. Only 
about half a pint out of three or four quarts of water leaving 
the body each day has been formed from the burning of food. 
For every hundred grams of protein about thirty grams of 
complex waste substances must be excreted by the kidneys. 

Calories. — So far we have been talking of the intake and 
output of the body expressed as material. We can also speak 
of income and outgo in terms of energy. If we are to do so, 
we must have a unit or measure to employ; the one which 
is almost always used is the calorie. You may have seen this 
word on the bill of fare of a restaurant where you read that a 
certain portion of food has a value of 100 or perhaps 200 
calories. Let us see just what is meant by such a statement. 

A calorie is a certain quantity of heat; it is the amount 
which will raise the temperature of a kilogram (1000 grams) 
of water one centigrade degree. Any pure substance which 
will burn is said to have a fixed fuel value. This is the amount 
of heat in calories set free when one gram of the substance is 
completely burned. So a gram of pure dry carbon (char¬ 
coal) burned to carbon dioxide gives always the same quan¬ 
tity of heat, about eight calories. One gram of alcohol 
burned to carbon dioxide and water gives seven calories. A 


PHYSIOLOGY AND HEALTH 


176 

gram of starch when completely burned gives about four 
calories. 

Carbohydrates and fats are oxidized in the body just as 
truly as when they are burned in the open. They produce 
the same amount of heat in one case as in the other. This 


fC 



.11 


ONE HUNDRED CALORIE PORTIONS OF FOOD 


cannot be said of protein, for the body does not burn it so 
completely as an actual fire would do. The wastes from pro¬ 
tein decomposition have a small fuel value, though the cells 
cannot avail themselves of it. These wastes may remind us 
of the cinders from a coal fire which usually have not given 
up all their energy and could be burned further in a hot flame. 

















INCOME AND OUTGO 


177 


Caloric requirements. — We have said that some of the 
tests made by engineers are much like those carried out by 
physiologists in their laboratories. The resemblance extends 
to this matter of fuel values. The engineer needs to know 
the amount of energy locked up in the coal or oil which he 
burns. This fuel value might be expressed in calories, just 
as in the case of foods, though a different measure is com¬ 
monly used. What you particularly need to understand is 
this: one form of energy can be changed into another. Heat 
is energy, and calories are heat units; but heat can be trans¬ 
formed in part to work, or mechanical energy. When we 
talk of the calories in the diet, we are not thinking simply of 
the power of the food to make us warm. Some of these cal¬ 
ories will warm us, but others will produce the force (work 
or movement) of contracting muscles. 

Suppose that a certain ration contains 100 grams of pro¬ 
tein, 100 grams of fat, and 400 grams of carbohydrates. We 
can-reckon the fuel value of this diet as follows: 


100 grams protein at 4 calories per gram 

100 grams fat at 9 calories per gram 

400 grams carbohydrate at 4 calories per gram 


400 calories 
900 
1600 


Total 2900 calories 


This is about the average requirement of an adult. A man 
who does heavy work day after day must have a much larger 
supply. Studies of the diets chosen by farmers show that 
they are accustomed to take about 3500 calories. The ra¬ 
tions of soldiers may provide 4000. Lumbermen who do the 
hardest possible work and endure the cold of the north woods 



PHYSIOLOGY AND HEALTH 


178 

in winter are reported to consume as many as 7000 calories. 
On the other hand, persons who take little exercise may find 
2500 calories sufficient, while 1800 may be enough for an in¬ 
valid lying in bed. 

Growing children need a great deal of food. You may 
have heard your mother express surprise at your own appe¬ 
tite. Some years ago a study was made of the food consump¬ 
tion at St. Paul’s School, Concord, New Hampshire. The 
investigators found out exactly how much of each article was 
served in the dining room and how much was left on the plates. 
These boys of high-school age were taking food to the value 
of 4350 calories. Even so, they were hungry between 
meals and ate food then equal to 650 additional calories. 
This made a daily total of 5000 and showed that the pupils 
received more food than farmers or even soldiers in active 
service. But we cannot say that they were overfed, for they 
were not overweight. 

The calorimeter. — One of the most interesting pieces of 
apparatus used by students of nutrition is the calorimeter. 
As the name suggests, this is designed to measure heat pro¬ 
duction. The largest calorimeters are made on a sufficient 
scale to be used upon human beings. A man is made to sit or 
lie in a small compartment. This is carefully ventilated, but 
its walls are so arranged that no heat escapes through them. 
The air which is drawn off by the ventilating system is re¬ 
placed by air having just the same temperature. The result 
is that the living body in the chamber does not rid itself of 
heat through the ventilating pipes or through the -walls. 
The air in the compartment then tends, of course, to grow 
steadily warmer, but it is kept at a steady temperature by 
coils of pipe in the calorimeter through which cool water is 


INCOME AND OUTGO 


179 


passed to absorb the heat. To do this, just as much heat 
must be carried away in the flowing water as the body gives 
to the air. 

The amount of water which passes through the coils is 
known. There are thermometers which show how much it is 
warmed. From the two readings one can calculate the cal¬ 
ories. Suppose, for example, that 800 liters of water went 
through the pipes and came away warmer by 3 centigrade de¬ 
grees than when it entered. The product of 800 and 3 is 
equal to the number of calories collected by the stream. This 
is 2400. 

We believe that all the energy set free in the body of a per¬ 
son finally appears as heat. The movements of the muscles 
simply add heat to the total. This can be made clear by tak¬ 
ing the case of the heart. This organ does a great deal of 
hard work. The high pressure that stretches the arteries is a 
sign of the energy which the heart has impressed upon the 
blood. But the blood returns to the heart with this store of 
energy exhausted; it has been changed to heat by friction in 
the vessels, particularly the very small ones. When the 
breathing muscles raise weight in expanding the chest, they 
do work; but when the body wall has settled back to its first 
position, this work is changed to heat. 

With calorimeters made on such a large scale that men 
can live comfortably within them for days at a time it is 
possible to measure the energy spent in various occupations. 
Often a bicycle has been set up in the chamber and the subject 
has ridden it by forcing the wheel around against the resist¬ 
ance of a brake. When a powerful man has done this for the 
largest part of twenty-four hours, the total energy set free has 
come close to 10,000 calories. This is more than the food 


i8o 


PHYSIOLOGY AND HEALTH 


for the day could be expected to furnish. Part of the energy 
in such cases comes from the burning of fat and other material 
drawn from the stores of the body. 

Variations in caloric content of foods. — When we com¬ 
pare different foods, we find that they are very unequal in re¬ 
spect to the number of calories which they can give us. The 
main reason for this is that some of them contain very little 
water and others a great deal. Water is generally good for 
us, but it does not give us calories. If a food is more than 
ninety per cent water, as is the case with a melon, you can see 
that there is not much in it which we can burn. One pound 
of butter represents as much energy as 42 pounds of lettuce. 
There is very little water in the butter; it is mainly fat, which 
has the highest fuel value of any type of food. The lettuce 
is about 95 per cent water, and a part of the solid fraction is 
indigestible; so there is not much energy supply in it. 

You are not to think when you hear such statements that 
foods with a low caloric value are objectionable. Fruits and 
vegetables, which belong to this class, are, on the contrary, 
very beneficial. A concentrated diet would not be whole¬ 
some. Bacon and eggs and candy might be suggested as a 
bill of fare that would give much energy in a small bulk and 
avoid waste, but it would probably disagree with most per¬ 
sons. On the other hand, men have lived in good health for 
long periods although eating practically nothing but vege¬ 
tables in quantities sufficient to furnish all the fuel needed 
by the system. 


Discussion 

1. Explain what is meant by income and outgo. 

2. What unit of weight is used in this chapter as a food measure? 


INCOME AND OUTGO 181 

3. How does the income of carbohydrates compare with that of 

fats and proteins in the diet of an average person? 

4. Explain why an adult often varies little in weight over a 

period of months. 

5. Name two waste products from the burning of fuel foods. 

6 . Discuss what is meant by calories. See if you can bring to 

class a menu which lists the number of calories in the vari¬ 
ous foods. 

7. Prepare from this menu a day’s diet for a farmer; a soldier; 

a clerk; an invalid; a growing boy. 

8 . In selecting a diet, what should one consider in addition to 

the number of calories? 

Problems 

1 . The average daily diet contains 100 grams of protein, 100 

grams of fat, and 400 grams of carbohydrate. What would 
be the equivalent in pounds? 

2. Assuming the protein in lean meat to be 20 per cent and the 

fat in butter to be 80 per cent, determine the quantities of 
strictly lean meat, butter, and pure starch necessary to fur¬ 
nish the desired number of calories of protein, fat, and car¬ 
bohydrate in one day’s diet. 


XIV 


THE TEETH 


Are the teeth alive? 

How are the teeth made? 

Do some people have harder teeth than others? 

What does the physiology of the tooth suggest concerning its 
care? 

You have probably never thought of Paul Revere as a den¬ 
tist, but the following copy of a printed advertisement from 
a colonial paper shows that such was the case: 

Whereas many Persons are so unfortunate as to lose their 
Fore-Teeth by Accident, and otherways, to their great Detri¬ 
ment, not only in Looks, but speaking both in Public and Pri¬ 
vate : — This is to inform all such, that they may have them re¬ 
placed with false Ones, that looks as well as the Natural, and 
answer the End of Speaking to all Intents, by PAUL REVERE, 
Goldsmith, near the Head of Dr. Clarke’s Wharf, Boston. All 
Persons who have had false Teeth fixt by Mr. John Baker, 
Surgeon-Dentist, and they have got loose( as they will in Time) 
may have them fastened by the above, who learnt the Method of 
fixing them from Mr. Baker. — Boston Gazette and County 
Journal, August 29, 1768. 

This advertisement is typical of those which used to be 
found in the days before there were any dental schools, when 
dentistry was thought of as a purely mechanical trade. The 

182 


THE TEETH 


183 

teeth were treated as though they were hard, lifeless struc¬ 
tures which had no effect upon the health of the rest of the 
body and upon which the general health of the person had no 
effect. 

How different is our attitude today! The dental school 
has made dentistry a profession which is a branch of medicine. 
We have learned that conditions arising from decayed and 
neglected teeth may produce serious ill effects upon other 
parts of the body. We find that the health of the body as a 
whole — particularly during those years when the teeth are 
being formed — has an effect upon the quality of the teeth. 
So close is this relationship between the function of the body 
and the health of the teeth that we may now properly speak 
of the physiology of the teeth in the same way that we would 
speak of the physiology of other parts of the body. Let us 
see what are the important facts about the origin and nature 
of the teeth. 

The formation of the teeth. — Before studying the origin 
of the tooth, it is well to recall its general structure. You 
remember that the hard substance known as dentine makes 
up the body of the tooth and that a still harder layer of enamel 
covers the part of the tooth that we see and reaches a little 
way below the soft tissue of the gums. There is a cavity at 
the center called the pulp cavity. 

The hard structure of every tooth is produced by soft, liv¬ 
ing cells. At the very beginning of tooth formation two 
layers of these soft, secreting cells appear near each other, as 
shown in the diagram on page 184. The cells of the outer 
layer come from those which are forming the structures of 
the skin and go down into the area of the gum, arranging 
themselves finally in a shape somewhat like that of a thimble. 


184 


PHYSIOLOGY AND HEALTH 



Courtesy of Lea & Febiger. 

A TOOTH IN PROCESS OE FORMATION 

This section through the gum shows a tooth at the time it is beginning 
to develop. In the center of the picture is a cap of soft tissue which 
forms the enamel, and growing into it is the soft tissue which forms the 
dentine. (From Fones’s Mouth Hygiene .) 

They then manufacture and secrete (on their inner surface) a 
substance which hardens to form the enamel, the hardest sub¬ 
stance in the body. At the same time the other layer of cells 



THE TEETH 


185 



A DIAGRAM SHOWING A CROSS SECTION OE A TOOTH 









































































186 


PHYSIOLOGY AND HEALTH 


from the deeper tissues has been pushed up into the thimble¬ 
shaped cap, and this layer of cells manufactures and secretes 
(on the outer surface) the substance which forms the dentine. 
Gradually, as the hard structures of the tooth are formed, 
these two layers of secreting cells are pushed farther and 
farther apart, so that when the tooth is complete, the cells 
which have formed the enamel lie around the outside of the 
top of the tooth and the cells which have formed the dentine 
line the pulp cavity. This whole process takes place, as 
every one knows, deep in the soft tissue of the gum, and the 
tooth is completely formed when it is erupted, or pushed 
through the gum. 

In the process of manufacturing both enamel and dentine, 
the living cells, which have become the tiny factories in this 
manufacturing process, are continually using two substances 
of prime importance. One of these substances is calcium, 
which is an important part of lime. The other substance is 
phosphorus, which you have heard of as being one of the sub¬ 
stances used in making matches. The little cell factories 
take these two substances from the blood and combine them 
with others to manufacture enamel and dentine. Obviously 
the blood must renew its supply of these substances used in 
the process of manufacture, and this means that calcium and 
phosphorous must be present in sufficient quantity in the 
child’s diet. If the factories get too little raw material to put 
into the product, the quality of the enamel and dentine is 
lowered. 

It has also been found that the body needs certain vitamins 
as well as calcium and phosphorus in order to be able to put 
together these two substances in proper form. Animals like 
guinea pigs produce hard strong teeth when they have a suit- 


THE TEETH 


1S7 

able diet, but the enamel and dentine of their teeth are of poor 
quality whenever they are fed upon a diet which is lacking 
such natural foods as leafy vegetables, milk, and other sub- 



OF TEETH 

Incisors 
Canine 

Molars 


TIME OF APPEARANCE 

7th Month 
9 th ” 
18th ” 

12th ” 
24th ” 


TEMPORARY SET 



Lower 

PERMANENT SET 


THE TEMPORARY AND PERMANENT SETS OP TEETH 

stances rich in minerals and vitamins. We see therefore that 
the quality or hardness of the teeth depends first upon the 
ability of the body to secure the necessary food substances 
used in the manufacture of the enamel and dentine, and sec- 















PHYSIOLOGY AND HEALTH 


188 

ond upon the ability of the body cells to carry out the manu¬ 
facturing process. A good illustration of this fact is seen in 
the results of severe diseases in children. In such cases the 
body is not well nourished and the tooth structure formed 
during the period of sickness is of very poor quality. Even 
in later life, if there is illness or if the diet fails to give the body 
enough calcium and phosphorus, the blood robs the teeth of 
some of these substances and they grow softer. 

The first teeth (baby teeth, or deciduous teeth) are already 
completely formed below the gum at birth. The second teeth 
(permanent teeth) have already started to form and con¬ 
tinue their development during early childhood. 

The first molars are sometimes called the ‘six-year molars.’ 
The second molars are sometimes called the ‘twelve-year 
molars,’ and the third molars, the ‘wisdom teeth.’ 

The diagram showing the arrangement of the baby teeth 
illustrates the important fact that the first tooth of the second 
set (the six-year molar) does not replace one of the baby 
teeth, but erupts behind those in the first set. 

The structure and arrangement of the teeth. — If we 
study the diagram illustrating the structure of a fully devel¬ 
oped tooth, we find at the center the pulp cavity, filled with 
soft tissue. Lining this cavity (next to the dentine) is the 
layer of cells which have manufactured the dentine. Within 
the tissue mass which fills the cavity is a bundle of nerves with 
many fine branches which end near the dentine-forming cells. 
A tiny artery comes into the cavity. It gives off branches 
which form capillaries and these, in turn, combine into a vein 
which carries blood back toward the heart. The dentine, 
when seen under the microscope, is found to be made of tu¬ 
bules packed tightly together in somewhat softer substance. 


THE TEETH 


Along the center of each tubule runs a tiny living fiber from 
the cell which produced it. 

The enamel is made of hard solid rods pressed tightly to¬ 
gether in a cementing substance. It used to be thought that 
there was no change of fluid whatever in the dentine and 



CHART OF THE FIRST TEETH 


enamel, but recent studies show that a foreign substance like 
a dye or lead which gets into the blood may find its way into 
the hard parts of the tooth. This means that the small 
amount of fluid which is in the tooth is changed from time to 
time and that the fluids of the body may thus influence the 
structure of the teeth. 








PHYSIOLOGY AND HEALTH 


190 

When we look at a tooth in the mouth, we see only the 
enamel, which covers the upper part. The diagram of tooth 
structure shows that the lower part (root) of the tooth is set 
firmly into a cementing substance and that the whole struc¬ 
ture is embedded in the bone of the jaw. 

When the teeth are perfectly formed, they lie with their 
sides so close together that there is no space for particles of 
food to get between them. The upper teeth and lower teeth 
fit together to make an ideal grinding surface, as shown in the 
illustration on page 191. 

The teeth of the second set are formed directly above or 
below those of the first set, and it is the growth of these perma¬ 
nent teeth which pushes out the baby teeth. During this 
process the attachments of the baby teeth are dissolved so 
that they fall out without any pain. Since the second teeth 
are closely following the first set, you can see that the latter 
act as guides to bring them into the proper places. It is im¬ 
portant, therefore, to take good care of the baby teeth, be¬ 
cause if they are lost too soon, the second teeth may be ir¬ 
regular. Whenever a tooth is pulled, it breaks the ‘shoulder 
to shoulder’ line, and the remaining teeth tend to grow in 
the direction of the opening to fill up this space. 

There are other reasons for irregular teeth. Sometimes 
the teeth appear to be too large for the space provided for 
them in the jaws and crowd each other out of position. The 
teeth and jaws need to be used vigorously in order that the 
stimulation provided by this hard work may produce a rapid 
growth. If, for some reason, the jaws are not used enough, 
they remain small and the lower jaw is likely to be too small 
in comparison with the upper jaw. Thumb sucking and the 
use of pacifying devices by babies tend to make the front 


THE TEETH 


191 

teeth stick out and to pull the jaws together so that they are 
too narrow. 

The physiology of living teeth. — The teeth, you now un- 



Courtesy of Lea & Febiger. 

A SET OF PERFECTLY FORMED TEETH 

Notice how the surfaces of the upper and lower teeth fit together to 
form a grinding organ. (From Fones’s Mouth Hygiene.) 

derstand, are not fixed and lifeless objects as people used to 
think. The living tooth has a continual stream of blood flow¬ 
ing through the capillaries in its pulp chamber and the fluid 
from this blood makes its way in and out of the hard struc¬ 
tures of the tooth. Teeth which are soft in childhood may 



PHYSIOLOGY AND HEALTH 


192 

become harder in later life if the individual has a proper diet; 
and teeth that are hard may become soft and easily broken if 
the diet becomes poor. The teeth are held in proper relation 
to each other under normal conditions, but may depart widely 
from this arrangement when some of the teeth are lost or 

when some other ab¬ 
normal condition in¬ 
terferes. In a moment 
we shall see two other 
close interrelationships 
between the health of 
the teeth and that of 
the body as a whole. 

Every one is familiar 
with the process of 
tooth decay, or caries, 
as the dentist calls it. 
A small black hole 
appears in the tooth 
and this cavity grows 
larger until it nears the 
pulp chamber. At this 
stage the tooth is sen¬ 
sitive to heat and to cold. It may begin to ache. In these 
cavities we always find bacteria. The mouth forms a warm, 
moist, dark place in which these bacteria may grow upon 
the particles of food in the tooth cavity or between the teeth. 
The bacteria turn starches and sugars into acids and the acids 
dissolve away the tooth structure, thus enlarging the cavity. 

If the decay goes deep enough into the tooth, the bacteria 
find their way into the pulp cavity where they multiply. The 



Courtesy of Lea Sr Febiger. 
ABSCESS FORMATION 


This X-ray picture shows an abscess, 
A, at the root of a tooth. (From Fones’s 
Mouth Hygiene.) 




THE TEETH 


193 


pulp of the tooth has become infected and an abscess may 
form in the pulp cavity or at the tip of the root. Sometimes 
these pockets of pus, or abscesses, can be detected only by the 
use of the X-ray. When an abscess is formed, the bacteria 
continue to multiply, and the white blood cells gather in this 
area to overcome the bacteria. Countless numbers of these 
white blood cells form a drop of pus. The living cells of the 
tissues are crowded apart, the circulation of the blood is in¬ 
terfered with, and swelling results. Some of the cells of the 
pulp die. The end of the nerve is destroyed and we say that 
we have a ‘dead 5 tooth. The bacteria continue to multiply 
and are carried away by the blood to other parts of the body. 
The condition is not only painful in itself and exhausting to 
the vitality of the person, but it is also dangerous to the gen¬ 
eral health, since the bacteria from this source may cause 
some forms of rheumatism and one type of heart disease. 
Abscesses are sometimes slowly developing infections which 
do not give pain; but they poison the system just the same, 
producing general poor health and lack of resistance and en¬ 
durance, as well as the diseases mentioned. Thus we see 
that decay not only interferes with the normal functioning 
of the tooth, thereby preventing the proper grinding of food, 
but that it also has serious consequences to the general health. 

How does this process of decay start? It used to be 
thought that particles of food left between the teeth would fer¬ 
ment and produce acid enough to dissolve away the enamel 
and begin the process of decay. We are not at all certain, 
however, that enough acid could be produced in the mouth to 
cause decay in the enamel if the latter were perfect in its 
construction. The lower animals rarely have decayed teeth, 
and tooth decay is rare among those people whose diet is made 


194 


PHYSIOLOGY AND HEALTH 


up of rough natural foods. Probably a race with a perfect 
diet and without diseases which upset the processes of tooth 
formation would never have decay. A perfect enamel would 
be formed and it would protect the softer structures of the 
teeth. 

Unfortunately the great majority of teeth (86 per cent of 



Courtesy of Lea & Febiger. 

THE STRUCTURE OF DENTINE 

This picture of dentine taken under the microscope shows the arrange¬ 
ment of tubules and fibers. (From Fones’s Mouth Hygiene.) 

all molars) are found to be imperfectly or incompletely cov¬ 
ered with enamel. There has been some defect in enamel 
formation and a tiny pit, or fissure (crevice), exists in the 
enamel, where, as a consequence, the softer dentine is ex¬ 
posed. These imperfections are too small to be seen with the 



THE TEETH 


195 


naked eye, but the dentist can find them when he examines the 
teeth carefully with the aid of a pointed instrument. Breaks 
in the enamel are also made sometimes by abusing the teeth 
in the attempt to crack nuts or to bite hard objects with them. 

It is now believed that nine-tenths of all tooth decay starts 
through these imperfections in the enamel and makes its way 
rapidly through the dentine, which is softer and less resistant. 
It has been found, in fact, that nearly all decay is prevented 
if these imperfections are mended as soon as the tooth erupts. 
Whenever new teeth appear, the child should go to the den¬ 
tist so that he can put small metal fillings into these pits and 
fissures. These fillings will be permanent, and when a child 
thus treated reaches adult life, his teeth will be free from 
decay. 

In the future this sort of prevention of tooth decay is likely 
to be the most important task of the dentist. At present it is 
one of our best weapons against decay. Sometime we may 
find out how our diet can be so much improved that the enamel 
will be perfect when the teeth are formed, but until then we 
must have all the imperfections mended as soon as possible 
after the teeth appear. It seems likely that the large amount 
of tooth decay at present is due to the fact that people did not 
understand this situation a generation ago. If from now on 
we should act upon our present knowledge regarding proper 
diet and the proper repair of pits and fissures, most of the 
tooth decay would disappear in one generation. It has been 
observed that candy seems to produce tooth decay. Candy 
does form acid which hastens decay once it is started. The 
most important objection against candy, however, is that it 
crowds out of the diet other foods, like fruit and vegetables, 
which ought to be eaten. 


PHYSIOLOGY AND HEALTH 


196 

Keeping the teeth clean. — You have been taught the 
proper method of brushing the teeth. Perhaps you are now 
asking yourself whether this is important. Yes, it is, and for 
several reasons. Once decay has started, it will progress 
more rapidly in a dirty mouth than in a clean mouth. Proper 
brushing of the teeth is also important for the health of the 
gums or soft tissues. When these are rubbed, the blood is 
made to flow through them briskly. This prevents their be¬ 
coming soggy and unhealthy. Sometimes the gums become 
infected around the roots of the teeth. They draw back 
from the teeth, becoming sore and bleeding easily. This con¬ 
dition is known as pyorrhea (a flow of pus). No particular 
tooth paste or powder will prevent it, but the regular process 
of brushing the teeth will help to keep the gums healthy. 
Moreover, brushing the teeth regularly improves the appear¬ 
ance and the breath. It makes the mouth feel so clean and 
comfortable that we should wish to do it even if it had no 
effect upon health. 

The bleeding of the gums is not necessarily a sign of pyor¬ 
rhea. The gums may have become tender with a poor circu¬ 
lation of blood because they have not received the stimula¬ 
tion which comes from regular brushing. Eating fruits and 
rough food may also help to clean the teeth and massage the 
gums. When there is no infection (pyorrhea), bleeding of 
the gums will soon stop if they are brushed gently. 

Another reason for brushing the teeth is to keep them 
white and free from stains. The yellow or dark color which 
one often sees on teeth is due to tartar, a substance deposited 
on the teeth when the saliva is slightly alkaline. The tooth 
brush keeps tartar from gathering upon the teeth. When the 
saliva is slightly acid, tartar does not gather; thus the 


THE TEETH 


197 


nature of saliva probably has an effect upon the growth of 
bacteria and the rate of tooth decay as well as upon the de¬ 
posit of tartar stains. Decay seems to progress more rapidly 
when the saliva is acid. 

In cleaning the teeth it is important that the brush should 
be of the right size and so constructed that the bristles will 
find their way between the teeth as you brush them with an 
up-and-down motion. The brush will be kept clean by rins¬ 
ing it after each use, preferably in hot water, and by hanging 
it where it will dry (in sunlight if possible), but not where 
dust or dirt will get on it. 

The chief substance in tooth powders and pastes is chalk, 
which has a mechanical cleansing action. This simple cleans¬ 
ing function is all that can usually be expected, and one should 
not be misled by excessive claims often made for particular 
kinds of tooth paste. Mouth washes also are often over-ad¬ 
vertised. A half teaspoonful of salt in a glass of water makes 
a very satisfactory wash. 

In addition to regular brushing, it is usually desirable to 
have the teeth cleaned once a year by the dentist or dental 
hygienist, who removes tartar deposits and cleans all the sur¬ 
faces of the teeth. 

Discussion 

1. Discuss the value of the following ways of caring for the 

teeth: 

a. Selecting proper diet 

b. Eating foods that need to be chewed 

c. Avoiding candy 

d. Eating fruit at the end of a meal 

e. Having irregular spacing of the teeth corrected 


igS PHYSIOLOGY AND HEALTH 

f. Avoiding mechanical injury 

g. Visiting the dentist 

h. Brushing the teeth 

2. At what ages do school children need to go to the dentist in 

order to get teeth inspected as soon as they come through? 

3. Explain the process of tooth formation. 

4. Name two substances used by the cells in the making of the 

teeth. 

5. Upon what factors does the hardness of the teeth depend? 

6. Explain the structure of a tooth. 

7. Make a list of the kinds of teeth, their number, and use. 

8. Why do we brush the teeth? 

9. Explain the process in tooth decay. What may be the re¬ 

sults? 

Activities 

1. Draw, on the blackboard, a diagram of a tooth with all its 

parts and explain it to the other members of the class. 

2. If possible, secure X-ray pictures of teeth and bring them to 

class. 

3. Make a list of girls and boys in the class who have all dental 

defects corrected (check by dental certificates from fam¬ 
ily dentist or clinic). 


XV 


HARMFUL SUBSTANCES 

Is more or is less work accomplished by a person who has taken 
alcohol? 

Is it true that alcohol helps endurance? 

What does the smoking habit cost the people of the United States 
each year? 

Why do athletic coaches prohibit the use of alcohol and tobacco 
while their pupils are in training? 

Alcohol 

When we think of substances which may enter the body 
and do it injury, we are likely to consider alcohol first of all. 
We are probably right in our belief that nothing else has done 
so much damage to so many millions of people. In the earli¬ 
est records of mankind and in the scriptures we find frequent 
references to wine. It is clear that man has had some kind of 
alcoholic beverage from the dawn of history and that grave 
dangers have always lurked within it. It was natural that 
wine should be the first alcoholic drink because it is produced 
by the fermentation of fruit juices when yeast cells grow in 
these sweet fluids. The microscopic cells of wild yeast are 
scattered widely in the dust and soil. When ripe fruit is un¬ 
broken, the fruit juices are protected by the skin or covering. 
When these juices are squeezed out, it is easy for wild yeast 
to get into the liquid. If the juices are then allowed to stand 


199 


200 


PHYSIOLOGY AND HEALTH 


for a few days, the yeast cells multiply and feed upon the 
sugar, with the result that wine is produced. One can see 
that it would have been easy for even primitive man to find 
out how to make wine. 

As civilization has developed, man has found other methods 
of making alcohol by the fermentation of sweet fluids. Malt 
liquors (beer and ale) are made by the fermentation of 
sprouting grains such as barley. The stronger liquors, like 
whiskey, brandy, rum, and gin, have gone through a process 
of distillation which increases the amount of alcohol in the 
beverage. Beer and ale contain from three to eight per 
cent of alcohol, wine from seven to twenty per cent, and dis¬ 
tilled liquors from thirty to sixty per cent. In all of these 
drinks it is the alcohol which produces the effect upon the 
body. 

As men have come to know more about the evil effects of 
alcohol, there has been a greater demand for temperance and 
for the prohibition of the manufacture and sale of these 
drinks. Several individual states, and finally the United 
States as a whole, have made the manufacture and sale of 
alcoholic liquors illegal. 

There are many aspects to the argument against the use of 
alcohol. Innumerable figures could be presented showing 
that drinking is responsible for many accidents in factories, 
on the highways, and elsewhere. When prohibition went into 
effect in the United States, there were relatively few automo¬ 
biles compared with the number we have at present. It is 
not difficult to imagine the increase in the number of accidents 
which would result if prohibition should be abandoned. 

Alcohol may also be a cause of .poverty. The Associated 
Charities of Boston reported in 1910 that, of 352 able-bodied 


HARMFUL SUBSTANCES 


201 


men who came to their attention because they failed to sup¬ 
port their families, 243 (65 per cent) were drunkards. 

Many crimes are committed under the influence of alco¬ 
hol. A special committee which studied crime in the United 
States found that drink was the sole cause of crime in 16.8 
per cent of the 13,402 convicts whose records were investi¬ 
gated. Moreover, drink was believed to have contributed to 
51 per cent of the crimes against person, 49 per cent of the 
crimes against property, and 47 per cent of all other crimes. 

These three grim spectres — accidents, poverty, and crime 
— are always clothed with sadness, unhappiness, and misery. 
Alcohol opens the door for them to enter the lives of men and 
women. Yet, important as these phases of the problem are, 
we shall not give them further attention in this book, but 
rather shall turn our attention to the effects of alcohol on per¬ 
sonal efficiency and health. 

The nature of alcohol. — Alcohol is a poisonous narcotic 
drug. In sufficient concentration it is poisonous to all living 
tissues of plants and animals. When pure alcohol is placed 
upon the skin, it produces itching, redness, and irritation. 
In its nature and its effects it is similar in many ways to ether. 
In large quantities it is irritating to the stomach and may 
cause that organ to secrete an excessive amount of mucus, 
resulting in sickness and vomiting. 

The effect of alcohol upon the nervous system. — The 
action of alcohol upon the nervous system is the most im¬ 
portant of its effects upon the various systems of the human 
body. We have just called it a narcotic drug. The action 
of a narcotic is to dull, stupefy, or put to sleep the cells of the 
central nervous system. People originally thought that al¬ 
cohol stimulated the cells of the brain to increased activity, 


202 


PHYSIOLOGY AND HEALTH 


but now it has been definitely proved that these cells are 
never stimulated, but always depressed, by alcohol. Let us 
see just what happens to the nervous system. 

The effect of alcohol is produced first in the feeling of well¬ 
being with (misplaced) confidence in physical power and 
mental ability. The person becomes excited; the face 
flushes; the eyes appear to brighten; and the pulse increases 
its beat. As the effect of the alcohol develops, the individual 
suffers a further loss of poise and self-control. There may 
be outbursts of anger, unreasonableness, or sentimentality. 
Still later, movement becomes uncertain; the walk becomes a 
stagger; the speech, a stammer; and finally deep slumber 
sets in. 

The effect of a large quantity of alcohol, which renders a 
person unconscious, is so similar to the effect of taking ether 
that the narcotic quality of alcohol is quite apparent. How 
is it that the first effect of a narcotic can be to make one feel 
stimulated and lively? The answer is that groups of cells in 
different levels of the nervous system are affected at different 
times and that the first cells to be affected are in those centers 
of the brain where judgment, poise, and discretion are gov¬ 
erned. It is thought by some that the connections between 
these cells are more delicate, so that their function is stopped 
first by the narcotic poisons. The lower levels of the nerv¬ 
ous system control the emotions and the reflexes. When rea¬ 
son, judgment, and discretion are impaired, emotion and 
movement are given freer play and a feeling of well-being 
and excitement results. The brain and the body may thus 
be less efficient even though the owner of the brain and body 
may feel more self-assured and competent than he usually 
does. 


HARMFUL SUBSTANCES 


203 


There are many illustrations of this situation. For ex¬ 
ample, Frankfurter made tests of the effect of alcohol on 
efficiency in typewriting. He says: “I had the feeling that 
the fingers ran faster than I could find the right place for the 
strokes. I often struck keys against my will, so that I had 
to make an effort to hold back a motion in order not to make 
a mistake at every letter.” He found that after taking alcohol 
he was unable to turn out as much work and that the work 
he did turn out had twice as many mistakes in it. 

Another experimenter showed that the efficiency of type¬ 
setters was reduced 8.7 per cent on days when they took half 
a tumbler of wine before beginning work. Schulz found 
that the amount of alcohol in about one and one-half glasses 
of wine would impair the vision of persons who had to dis¬ 
tinguish between shades of colors. 

Vogt experimented with the effect of alcohol by committing 
Greek poetry to memory, sometimes without alcohol and 
sometimes after having taken some. It took him about five 
times as long to learn twenty-five lines on the days when he 
had taken alcohol as on the days when he had not. A few 
months later he found that it was more difficult to relearn the 
lines committed to memory on the days when alcohol was 
taken. 

Other scientists have found that more mistakes were made 
in reading or in adding a row of figures after taking even 
a small quantity of alcohol. The intellectual ability and the 
simpler mental processes as well as the memory were impaired, 
and this reduced efficiency lasted for several hours after the 
alcohol had been taken. All these are clear-cut evidences of 
the narcotic effect which alcohol exerts upon the nervous 
system. 


204 


PHYSIOLOGY AND HEALTH 


If large or repeated doses of alcohol are taken, its injury 
to the cells of the nervous system becomes permanent. Cells 
taken from the brains of men or animals after death show, in 
cases where the individual has been poisoned for a long time, 
that changes have taken place in both the body and the fibers 
of the cell which make these structures look different under 
the microscope. Such a brain injury resulting from the ef¬ 
fect of alcohol as a nerve poison explains the development of 



Courtesy of Massachusetts Institute of Technology. 

A WINNING LIGHT CREW 
Their training rules were not broken. 

alcoholic hallucination, delirium tremens, and other forms of 
alcoholic insanity in persons who drink heavily. 

The effect of alcohol on the circulatory system. — One 
of the first effects of the weakening of nerve control by alcohol 
is to increase the rate, though not the strength, of the heart 
beat and to permit the dilation in the small blood vessels of the 
skin which shows itself in the flushed and perspiring face of the 
drinker. The presence of an increased quantity of warm 
blood in the skin gives him the feeling of warmth and comfort 





HARMFUL SUBSTANCES 


205 


after drinking and has led to the mistaken idea that alcohol 
would have a warming effect upon a person exposed to extreme 
cold. Nothing could be farther from the case. Sending the 
blood into the skin in this way causes the body to lose heat 
very rapidly. The heat-regulating mechanism is rendered 
less effective by the drug and as a consequence a man who 
has just taken alcohol may freeze to death in temperatures 
which would produce a less serious effect on the abstainer. 

It is well known that alcohol lowers the endurance. This 
fact is explained by the rapid heat loss just described and by 
the ill effect on the nervous system previously mentioned. An 
example of lowered endurance which is often quoted is the 
experiment of General Wolseley, of the British army. Dur¬ 
ing a series of marches which occupied several weeks, three 
groups of marchers were formed. The first group was given 
a daily ration of whiskey, the second a daily ration of beer, 
and the third only water. The whiskey group marched away 
fastest and took the lead, but before long the beer squad over¬ 
took and passed them. The water squad started out at a 
steady, moderate gait, but they kept it up. Eventually they 
overtook and passed, first the whiskey squad, and then the 
beer squad, and reached the end of the extended march long 
before either of the other groups. 

Alcohol and infectious disease. — It has long been known 
that persons who use alcohol have less chance of recovering 
from many of the infectious diseases. Drinking causes tu¬ 
berculosis to progress much more rapidly. Alcoholics have 
a poor chance of recovering from pneumonia. Many other 
infectious conditions that would not be fatal in a normal in¬ 
dividual may prove fatal in the person who has used alcohol 
habitually. Animals that have been exposed to alcohol have 


206 


PHYSIOLOGY AND HEALTH 


been found to be more susceptible to blood poisoning and 
pneumonia. The reason for this lowered resistance is not 
clear; it may be due to the inactivity of the white blood cells 
or to a lowered ability of the cells of the body to produce sub¬ 
stances needed to fight the disease. 

Alcohol and the death rate. — Data from various sources 
indicate that diseases other than the infectious ones, espe¬ 
cially diseases of the kidney and liver, are more common 
among drinkers than among abstainers. Many facts have 
been brought forth to show the relationship between drinking 
and the death rate. 

In his book on Alcohol and Longevity, Dr. Pearl says 
(p. 122) of the people whose records he studied that at all 
ages from thirty on, the survivorship line for heavy drinkers 
lay well below that of either abstainers or moderate drinkers. 
At a point between 58 and 59 years of age, one-half of the 
original heavy drinkers starting together at age thirty had 
passed away. But it was not until ten years later (between 
68 and 69) that one-half of the abstainers and the moderate 
drinkers had died off. He concluded that “clearly heavy 
drinking as defined in this book definitely and seriously im¬ 
pairs life duration in males.” 

In his book on The Effect of Alcohol on Longevity, Dr. O. 
H. Rogers reviews the experience of insurance companies in 
North America, Europe, and Australia, and he probably 
voices the experience and attitude of the average insurance 
company when he says: 

There appears to be no limit within which alcohol may be en¬ 
tirely harmless. It is as if there were a direct relation between 
the amount of alcohol used and the amount of damage done to 
the body. The evidence is strong also that the damage done per- 


HARMFUL SUBSTANCES 


207 


sists a long time after it has been discontinued. Any one who 
uses alcohol now, or has used it in the past, is a less desirable 
risk, all other things being equal, than a total abstainer, and his 
undesirability is in proportion to the freedom with which he has 
used the drug. 


Tobacco 

The nature and extent of the tobacco habit. — Most of 
the tobacco now manufactured is used for smoking. Snuff 
and chewing tobacco are not in popular demand at the present 
time. Snuff was a powder made from tobacco, and it was 
drawn into the nostrils from a pinch of the stuff taken up be¬ 
tween the fingers. The so-called ‘chewing tobacco’ is made 
by pressing tobacco leaves together into a cake, or plug. A 
few persons still have the uncleanly and unsightly habit of 
chewing tobacco, but for the most part snuff-taking and to¬ 
bacco-chewing have disappeared. We may consider the sub¬ 
ject, therefore, from the standpoint of the very common habit 
of smoking. 

One sometimes wonders why smoking has become so gen¬ 
eral a habit among adults. The usual answer is that it is a 
drug habit. The plant, as you know, contains the substance 
nicotine, which is a narcotic and habit-forming drug like 
alcohol and opium, although weaker and not so dangerous in 
its effects upon the human system. It is doubtless the crav¬ 
ing for this drug, to which the system has become accustomed, 
which makes it so hard to drop the habit of using tobacco. It 
is certainly true, however, that smoking is a social habit and 
a nervous habit as well as a drug habit. If this were not true, 
probably many persons would never learn to smoke, because 


208 


PHYSIOLOGY AND HEALTH 


it is almost as difficult for some persons to take up the habit 
as it is for them to drop it. 

Considerable discomfort is likely to be felt in one’s first 
attempts to smoke. The stomach may be upset; the head 
aches; the throat is irritated; and a disagreeable taste is left 
in the mouth. These unpleasant results often persist for a 
long time. Why, then, you ask, should one continue the at¬ 
tempt to smoke? It is usually because others are smoking 
and a person feels that he wants to be like others. He is 
foolish enough to do something which is uncomfortable be¬ 
cause he does not wish to refuse an invitation to join the 
others. 

Many persons smoke because they are nervous and want 
something to do. They get no special enjoyment from to¬ 
bacco beyond that of holding the pipe, cigar, or cigarette in 
their hands or between their lips. They might be just as 
happy with an unlighted cigarette, a piece of chewing gum, or a 
piece of hard candy on a stick if that happened to be in style. 

We are concerned in this book chiefly with the problem of 
the ill effects of tobacco upon the body, but we could find 
strong arguments against the widespread habit of smoking, 
upon purely financial grounds, if we were to stop to consider 
the amount of money spent each year for tobacco. The fact 
that the people of the United States pay over two billion dol¬ 
lars a year to keep up the habit of smoking may mean little to 
us because we find it difficult to imagine so large a sum of 
money. It means more to us when we stop to think that the 
amount paid for tobacco would be nearly twenty dollars a 
year for every man, woman, and child in the country. The 
money spent for tobacco in this country each year would run 
our public schools. 


HARMFUL SUBSTANCES 


209 



Figures from another source show us that actually millions 
of dollars are lost in this country each year by fires which are 
caused by smokers throwing down lighted matches or the 
burning stubs of cigarettes or cigars. Certainly the average 


A BROAD JUMP 

A famous athlete making a broad jump record of twenty-five feet, 
six inches. 

young person can ill afford to develop a habit which will cost 
him fifty or one hundred dollars a year, a sum which makes a 
good start toward the cost of a year in school or college. We 
find in smoking a habit which is useless and expensive to the 



210 


PHYSIOLOGY AND HEALTH 


individual and which is so general that it involves a huge 
waste of money each year for the nation. 

The effect of tobacco upon the health and efficiency of 
the body. — Tobacco has never been known to increase ef¬ 
ficiency in any activity or to cure any of the ills of the body. 
In the first use of tobacco its poisoning effects are clearly ap¬ 
parent. As smoking becomes a habit, these effects are not 
so marked. The body has improved its ability to withstand 
or tolerate this particular poison. This does no*t mean, how¬ 
ever, that the ill effect of the drug is lost; it is a characteristic 
of the body that it can accustom itself in some ways to in¬ 
creasing doses of an injurious drug. 

Athletic coaches in colleges and high schools have long 
known that tobacco interferes with athletic success. Physi¬ 
ologists agree that the effects of tobacco upon the appetite, 
digestion, nervous system, and general body functions of the 
growing boy or girl interfere with health and with growth. 
This injurious effect of tobacco upon development is seen even 
at the college age. Studies by Dr. Hitchcock at Amherst 
College and by Dr. Seaver at Yale University show that the 
increase in weight, height, and lung capacity while in college 
is significantly greater among men who do not smoke than 
among men who do. 

Most of our knowledge about the physiological effects of 
tobacco comes from careful scientific study and observation. 
One of the experiments most widely quoted is that carried out 
by Dr. George Fisher and Professor Berry, of the Interna¬ 
tional Y. M. C. A. College, at Springfield, Massachusetts, and 
reported in Dr. Fisher’s book, The Physical Effects of Smok¬ 
ing. Their studies were made upon fifteen young men, eight 
of whom were moderate smokers. They found that the nor- 


HARMFUL SUBSTANCES 


211 


mal heart rate among the smokers was higher than among 
the non-smokers, and that the rate of heartbeat increased for 
each man upon smoking and did not come back to normal for 
about a quarter of an hour after he had stopped smoking. 
The average heart rate at the fifteenth minute after smoking 
was 11.2 beats greater than the average normal heart rate. 
Both the habitual smokers and the non-smokers showed a 
reduced ability in pitching a baseball after smoking. Dif¬ 
ferent individuals were affected to a different degree, but all 
showed a greater loss in accuracy in pitching a baseball after 
smoking two cigars than after smoking one. The non- 
smokers lost ability more rapidly when smoking between 
pitching contests, and gained ability more rapidly when all of 
the men rested without smoking between pitching contests 
thirty minutes apart. This study shows that control of physi¬ 
cal activity is poorer after smoking, and it shows that the 
habitual smoker does not get used to tobacco because his skill, 
as well as that of the non-smoker, was decreased after 
smoking. 

There have been several studies of the effect of smoking 
upon the heart. During the World War, Captain Parkinson 
and Dr. Koefod studied the effects of cigarette smoking upon 
healthy men and upon cases of soldier’s heart. ‘Soldier’s 
heart’ is the name given to an illness the symptoms of which 
are breathlessness after exertion; pains in the chest; rapid, 
irregular heart action; giddiness; and exhaustion. The ob¬ 
servations of these scientists show that “in health the smok¬ 
ing of a single cigarette by an habitual smoker usually raises 
the pulse rate and blood pressure perceptibly and these ef¬ 
fects are a little more pronounced in cases of soldier’s heart. 
Moreover, the smoking of a few cigarettes can render healthy 


212 


PHYSIOLOGY AND HEALTH 


men more breathless on exertion, and manifestly does so in a 
large proportion of these patients. 

“Excessive cigarette smoking is not the essential cause in 
most cases of ‘soldier’s heart/ but, in our opinion, it is an 
important contributory factor in the breathlessness and pre¬ 
cordial pain [pain over the heart] in many of them.” 

It has long been known that heavy smoking will cause pain 
around the heart and cause the heart to skip beats. Doctors 
prohibit smoking to patients with certain types of heart 
disease. 

We have seen in the experiments on baseball pitching that 
smoking interferes with the ability of the nervous system to 
control the muscles perfectly. Another effect on the nervous 
system is to be seen in the interference with vision which is 
produced by tobacco. We do not mean the smarting and 
weeping of the eyes when smoke geffs into them. That is 
caused directly by the irritating effects of the smoke upon the 
moist surface of the eye. Wholly apart from this, heavy 
smokers often complain of specks before the eyes and some¬ 
times of a sense of pressure in the head. 

The habit of smoking spread rapidly during the War be¬ 
cause the soldiers were sent cigarettes and were given tobacco 
in the army ration. Of course, one reason for this was that 
the soldier’s life was a hard life, and if he enjoyed smoking, 
people thought he should have that enjoyment. However, 
people who had heard that smoking was injurious to the ath¬ 
lete began to wonder whether tobacco really did any harm 
after all if soldiers could use it so freely. We get a true state¬ 
ment of the facts from the following quotation from Major 
Lelean of the British army in lectures delivered before the 
Royal Army Medical College: 


HARMFUL SUBSTANCES 


213 


To take now the next item which comes on the ration list — 
tobacco. The effects of smoking on the heart and on the quality 
of the pulse are well shown by pulse tracings. Without going 
into the question of such various objectionable ingredients in 
tobacco as nicotine and the more harmful furfural, one may say 
that excess of smoking, particularly of cheap cigarettes, produces 
tachycardia [rapid heart], muscular relaxation, and diminu¬ 
tion of visual acuity [lowered powers of clear vision]. These 
conditions result in ‘shortness of wind,’ which is bad for march¬ 
ing, and produce muscular tremor and loss of effective sight, 
which it scarcely need be said are worse for shooting. 

Major Lelean goes on to say that the soldier who smokes 
a pipeful of tobacco upon reaching camp or before he turns in 
at night may get some comfort or quieting effect from it, but 
tobacco as well as alcohol lowers efficiency and should be for¬ 
bidden to soldiers on the march because it causes tremor and 
rapid heart. 

When we come to sum up a careful study of the scientific 
facts about tobacco, we cannot produce any evidence that it 
will do anything for the support and upbuilding of health. 
On the other hand, tobacco has to its discredit the production 
of the following unfavorable effects upon the body: rapid 
beating of the heart, pain in the region of the heart, a dis¬ 
turbance of blood pressure, shortness of breath, sleeplessness, 
acid dyspepsia (an acid condition of the stomach causing 
definite discomfort), catarrh of the nose and throat, inter¬ 
ference with athletic ability, and interference with the ef¬ 
ficiency of vision. 

There is no question as to the harmful effects of the im¬ 
moderate use of tobacco. Habitual smokers generally admit 
these evils. It is true that its effects are more severe upon 


214 


PHYSIOLOGY AND HEALTH 


some individuals than upon others. It is also true that mod¬ 
erate smoking does not produce all of these ill effects; but the 
use of tobacco, like the use of alcohol, seldom stays moderate, 
and the young man or woman who wants to stay physically 
fit will do well to keep away from tobacco. 

Tobacco and scholarship. — From the standpoint of schol¬ 
arship all of the evidence is against the use of tobacco. There 
is no indication that tobacco improves mental efficiency and 
there is evidence that the mental efficiency of many individ¬ 
uals is definitely lowered by using tobacco. In a high-school 
study made by Richard Sandwick it was found that 7 7 boys 
who were non-smokers had an average grade of 84.5; 24 boys 
who had quit smoking had an average grade of 80.5; 55 boys 
who were habitual smokers had an average grade of 76; and 
45 habitual smokers who had recently left school had an aver¬ 
age grade of 69. 

In a study of 950 pupils in the schools of Bloomington, 
Indiana, it was found that smokers did poorer school work, 
failed more often, and were disciplined more frequently than 
non-smokers. 

At Antioch College, Professor Earp found that there were 
more non-smokers than smokers among the students having 
highest grades. A two-year study by Dean Hornell at Ohio 
Wesleyan University showed that non-smokers attained 84 
per cent of the high grades and smokers only 16 per cent of 
them. Dr. Seaver found that smokers averaged 15 months 
older on entering Yale than did non-smokers. Professor 
Fink, of Miami University at Oxford, Ohio, made an exten¬ 
sive study of the scholastic record of young men in various col¬ 
leges and universities from which he figured that relative 
scholastic ability was indicated as follows: non-smokers 108.2, 


HARMFUL SUBSTANCES 


215 

light smokers 103.3, medium smokers 99.7, and heavy 
smokers 77.7. 

From the standpoint of scholarship it does not matter very 
much whether this reduced ability is produced by the direct 
effect of the tobacco or by the indirect effect of the mental 
laziness and inattention which are apt to come with smoking. 
The argument is against the smoking habit in either case. 

Tea and Coffee 

These beverages are greatly enjoyed in almost all parts of 
the world and probably, so far as our own country is con¬ 
cerned, by the majority of the population. In a case like this 
it is not easy to prove that all these persons would be better 
off if they were to give up their practice. There are some 
who would be better off, and they admit it themselves. The 
two beverages seem quite unlike, but the same drug is present 
in both. It is the compound known as caffein. 

Tea and coffee are said to be true stimulants. This means 
that they give those who use them extra working power. The 
difference between coffee and alcohol is one which it is im¬ 
portant to understand. Both give the feeling of refreshment 
and confidence. But in the case of coffee the user may do bet¬ 
ter work. In the case of alcohol we know he is deceived as 
to his own condition. He shows a poorer performance even 
when he is sure that he is at his best. “Wine is a mocker,” 
wrote the author of one of the passages in the Old Testament 
many centuries ago, and modern science leads to the same 
conclusion. 

Since tea and coffee are genuine stimulants, they are valu¬ 
able when difficult situations have to be met — for instance, 


2l6 


PHYSIOLOGY AND HEALTH 


when one has to keep awake for a long period to attend to a 
person who is sick. Because of this, it is not wise to take 
them regularly when no special need exists. They will be 
more helpful in a time of trouble if they have not been in con¬ 
stant use. 

Boys and girls should not drink tea or coffee. Their 
nervous systems do not need stimulation. Ordinarily they 
are not obliged to work and worry when it is time to rest. 
They ought not to fight against sleep in the evening, but 
rather to give way to it when sleepiness comes over them. 
In later life when heavy responsibilities must be met, tea 
and coffee may be real aids, but in general they should be kept 
in reserve most of the time. 

Chocolate and cocoa are less stimulating than tea and cof¬ 
fee, but are rather hearty foods for some persons. 


Medicines 

Medicines are not treated in this chapter on “Harmful Sub¬ 
stances” because they are injurious, but because they are 
often used improperly. The old-time doctor gave a great 
deal more medicine than most doctors do in our day, although 
some of the drugs recently prepared are of great value. We 
have mentioned insulin, for instance, which relieves the con¬ 
dition of diabetes in such a marvelous way. The antitoxin 
generally used to cure diphtheria is another example. 
Such drugs as these are not likely to be used except under the 
doctor’s direction. What we ought to warn against is the 
taking of various medicines without his advice. Many per¬ 
sons frequently do this. 


HARMFUL SUBSTANCES 


217 


Sometimes the medicine is selected after consulting the 
druggist. The druggist may know a great deal about his 
stock, but he cannot know much about the patient. Some¬ 
times the preparation is taken on the recommendation of a 
friend. Often it is something which has been advertised with 
all kinds of testimonials, a patent medicine. Many of these 
patent medicines are frauds. Some have been sought 
after because they have contained plenty of alcohol, 
though they are much more carefully regulated by law than 
was the case a few years ago. Some of them are mixtures 
which have some possible use. But in this case they are al¬ 
ways unnecessarily expensive and usually the directions en¬ 
courage one to go on taking them for a long time. 

It is true of many drugs that the body becomes more and 
more indifferent to them when they are used again and again. 
Larger doses may have to be taken to get the effect desired. 
This is especially true of the most hurtful of all drugs, the 
habit-formers, of which morphine is the worst example. 
This compound is made from opium, which is a product of the 
poppy plant. 

Every precaution must be taken against the sale of mor¬ 
phine. Persons who have begun to use it can seldom give it 
up without serious suffering. In their early experiments with 
it they find that it gives them pleasure; later they can only 
say that they are miserable without it. Health is wrecked 
and character is lost under its influence. 

Other habit-forming drugs exist, but it is not necessary to 
mention them individually. It can be said of all that they 
are ruining lives and that there is no more wicked business 
than that of furnishing them to their victims. Decent people 
are in full agreement as to this. 


218 PHYSIOLOGY AND HEALTH 

Discussion 

1. Why has the United States made the manufacture and sale 

of alcoholic liquors illegal? 

2. Describe the effect of alcohol upon the nervous system. 

3. Explain the action of alcohol on endurance and skill. De^ 

scribe any one of the experiments. 

4. In what manner does alcohol affect the circulatory system? 

5. How is alcohol related to lowered resistance to disease? 

6. Give data from this text to show that alcohol may affect the 

death rate. What do insurance companies believe on this 
point? 

7. What is the effect of tobacco upon the health and efficiency 

of the body? What conclusions about tobacco were 
made from the study of its effects upon soldiers? 

8. Sum up the unfavorable effects of tobacco smoking under 

the headings of effects on the body, on scholarship, and 
on the pocketbook. 

9. Why is different advice given to adults than to young folks 

in the use of coffee and tea? 

10. What dangers lie in the use of patent medicines? 


XVI 


INTERNAL SECRETIONS 

What are the powerful substances called internal secretions? 

What is the thyroid gland, and what is its influence upon the 
body? 

What has made some men giants and others dwarfs? 

Let us now take up a subject which is not so familiar as 
most of those we have been talking about, but which is not 
particularly difficult. It is something which we are learn¬ 
ing more and more about in these days and it is interesting 
the doctors a great deal. This is the subject of internal se¬ 
cretions. When we discuss internal secretions we are trying 
to give facts with respect to the way in which various organs 
influence others or affect the condition of the body as a whole. 

It is plain that each organ takes supplies of many sorts 
from the blood and gives various compounds back to the 
blood in exchange. We are entirely accustomed to thinking of 
the reception of oxygen by the muscles and the return of car¬ 
bon dioxide from their fibers to the passing blood stream. It 
is certain that other materials are given and taken by the 
blood on its round, and these are bound to differ in the differ¬ 
ent tissues of the body. The blood always contains a mix¬ 
ture of all the peculiar contributions of all the tissues, doubt¬ 
less a great number of entirely distinct substances. In other 
Words, the make-up of the blood depends on the united ac¬ 
tivities of all the organs in the body. 


219 


220 


PHYSIOLOGY AND HEALTH 


The pancreas. — Of these organs there are a few that de¬ 
serve special mention because their influence is so important. 
One of them has, in fact, already been given some attention. 
When we were talking about the use of food by the body, we 
said that the muscles cannot use sugar as a fuel without the 
aid of the pancreas. It was explained then that this struc¬ 



ture is something more than a gland providing a digestive 
secretion; some of its cells give their manufactured product 
to the blood instead of to the intestine. This product is in¬ 
sulin and, as you already know, the failure of these cells to 
produce it results in diabetes. 

The thyroid. — One of the best known of the organs of in¬ 
ternal secretion is the body called the thyroid. This is a flat 
structure lying across the trachea in the front of the neck and 









INTERNAL SECRETIONS 


221 


below the larynx, or Adam’s apple. The thyroid is some¬ 
times enlarged; you may have seen people with a swelling at 
this place. Such a swollen thyroid is called a goiter. There 
is no doubt that the thyroid makes a most precious contribu¬ 
tion to the blood, and it has long been known that when it 
fails in its duty the effect is serious. 

Occasionally a child is born whose thyroid does not act in 
the normal way. Such a child fails to develop and remains a 
deformed dwarf. Even if he lives for many years, there is 
neither mental improvement nor bodily growth. The un¬ 
fortunate person is called a cretin. We know that the thyroid 
is at fault in such cases, because if a cretin is fed proper 
amounts of thyroid material from the lower animals, a re¬ 
markable improvement in general condition at once begins. 
If the patient is not too old, his body grows rapidly and be¬ 
comes more shapely. Hardly any medical discovery has 
been more impressive than this. Something evidently goes 
out from the cells of the thyroid by way of the blood which 
has the greatest influence on the welfare of distant parts. 

The thyroid gland may also fail to maintain its proper 
service in later life. When this occurs in persons who have 
had a normal development, they do not actually go backward 
and become cretins, but they show definite signs of the lack of 
the thyroid secretion and are benefited by thyroid feeding. 

As it is possible to have an unfortunate failure of the thy¬ 
roid, so is it possible to have it too active. In fact, this is the 
more common trouble. Too much thyroid secretion upsets 
the state of the system. Extra thyroid activity produces 
restlessness and excitability. With too little thyroid the skin 
is cool and dry; with too much it is warm and moist. With 
too little, the weight is high for the size of the skeleton; with 


222 


PHYSIOLOGY AND HEALTH 


too much, there is loss of weight. In the first case there is a 
small appetite; in the second case, a very large one. The 
heart of the cretin beats slowly, while an overactive thyroid 
speeds up the pulse. In gen¬ 
eral it appears that the thy¬ 
roid product has the property 
of making the life processes 
go on more rapidly. Ex¬ 
tracts of the organ have been 
used for the reduction of 
weight; they may be said to 
open the drafts and cause the 
body to burn its stored fuels 
at an increased rate. 

The substance which comes 
from the thyroid and has such 
far-reaching effects has been 
prepared in a very pure form. 

A surprisingly small dose of it 
will make a difference in the 
rate of the bodily processes 
over a period of several days. 

This compound contains 
the element iodine, some¬ 
thing which is hard to find A GIANT AND A dwarf 
elsewhere in the system. The • w hat ductless gland is concerned 
thyroid cannot make this 

valuable material unless a supply of iodine can be had. 
Salts of iodine exist in sea water. Traces of these salts 
are probably carried by the winds for a considerable distance 
inland. They enter our food and drinking water. People 




INTERNAL SECRETIONS 


223 


who live far from the sea coast and who seldom have sea 
food to eat may fail to get even the minute quantity of 
iodine which they need. This seems often to be true of 
persons who live near the Great Lakes. 

Boys and girls who are short of iodine may have enlarged 
thyroids without the symptoms just described for those with 
overactive glands. In such cases the gland is not producing 
too much of its proper secretion; its enlargement is more truly 
the sign that it has to work hard to make a barely sufficient 
amount. This sort of thyroid enlargement is called a simple 
goiter. It can almost always be corrected by making sure 
that a trifling amount of iodine is included in the diet. Special 
brands of table salt containing a slight trace of iodine can be 
used. 

The pituitary body. — Normal growth and development 
depend on certain other organs besides the thyroid. It is 
curious to learn that the skeleton has its proportions deter¬ 
mined by the working of a very insignificant-looking structure 
attached to the under surface of the brain. This is the pitui¬ 
tary body. We know that if it does not do its full duty dur¬ 
ing the years of growth, the individual will not reach normal 
size. On the contrary, it has often overstimulated the growth 
of the bones and produced giants like those we see in the 
circus. Examination by the X-ray of the skulls of men who 
stand eight feet tall has shown an enlargement of the pituitary 
body. 

The adrenal body. — Immediately above each kidney there 
is a small organ called the adrenal body. It has long been 
known that the adrenals are necessary to life. When they 
are destroyed by disease, death results. There are two kinds 
of tissue in the adrenals, and this made it hard to discover 


224 


PHYSIOLOGY AND HEALTH 


their function. They have a powerful internal secretion, 
called adrenalin , which they seem to add to the blood on spe¬ 
cial occasions. 

A number of striking effects are produced when a prepara¬ 
tion of adrenalin is added to the blood of an animal, and the 
effects are much the same whether the compound has been 



This diagram shows the position of the adrenal glands, the kidneys, 
and their blood vessels. 

introduced from outside or secreted by the animal’s own 
adrenal bodies. 

Adrenalin stimulates the heart to beat hard and fast. It 
tightens the small blood vessels of the digestive tract, causing 
the blood to take other paths. It affects the cells of the liver 
in such a way that the glycogen stored in that large organ is 
turned into sugar and given out to circulate with the blood 
stream. It brings to a standstill the movements of the intes- 


















INTERNAL SECRETIONS 


225 


tine. Besides these general effects, there are various others 
of a more local sort, such as an enlargement of the pupils of 
the eyes. 

Physiologists have pointed out that the chief effects of extra 
adrenalin in the blood are just those which will help an animal 
in a struggle. Much depends on the power and endurance 
of the heart at such a time, and here we have a stimulant fur¬ 
nished for that organ. A great supply of blood is needed in 
the muscles, and the business of digestion can be postponed 
to a more favorable time; here is an agent which turns blood 
away from the digestive system and into the muscles. 
Adrenalin is known to increase the working power of the 
muscles and to delay the coming of fatigue. 

Experiments have shown that when an animal is excited, 
adrenalin makes its appearance in the blood. The tissue 
which manufactures it has been brought into increased activ¬ 
ity. The same is true of man. An exciting occasion is prop¬ 
erly a time when something of an active nature is to be done. 
In the case of the lower animals it may be a time for attacking 
an enemy, for defense against one, or for flight at the highest 
speed. In any of these courses there is need for the assis¬ 
tance which adrenalin has been found to give. What is called 
The strength of desperation’ may be the power given to the 
system by this remarkable secretion. By its presence the 
circulation is adjusted to give support to the working muscles, 
the muscles themselves are made more enduring, and an ample 
supply of sugar fuel is brought to them. 

If a person becomes excited and then finds nothing to do to 
work off the excitement, these bodily changes set up by the 
excitement fail to accomplish any good. Some physiologists 
think that they are actually harmful; that an excited person 


226 


PHYSIOLOGY AND HEALTH 


who has not found any course of action is like an automobile 
with its engine racing and out of gear. 

Civilized man has to control himself in many situations in 
which his savage ancestors would have fought or taken to 
flight. It is not enough, you see, to control action; it is im¬ 
portant to control feeling and emotion. This is a very hard 
rule. When we do get excited and still do not find it neces¬ 
sary to fight or run, it is probably best to set ourselves to some 
useful work in which energy can be spent. 

The spleen. — There are a number of other organs which 
are believed to have internal secretions. Some have to do 
with development and so have a gradual influence lasting for 
years. Others seem to be active on special occasions, like the 
cells which produce adrenalin. It would be confusing to tell 
about them all. Now and then an organ comes to our notice 
which might be expected to have an internal secretion, but 
which has not been shown to help the body in this way. This 
has been the case with the spleen, which has long been a puzzle 
to students. 

The spleen is a good-sized mass of tissue of a deep red color. 
It is in the abdominal cavity, and about level with the lower 
ribs on the left side. It is, therefore, to the left of the stom¬ 
ach. The spleen has a large supply of blood and returns it 
to the portal system. It contains a good deal of muscular 
tissue and is found to be slowly swelling and shrinking minute 
by minute. Everything about the spleen suggests that it is 
occupied with some important office, but this has not been easy 
to prove. No very active extract can be made from it by 
chemists. It can be removed and the animal will do well 
without it. 

Recently it has been shown that the spleen is a storehouse 


INTERNAL SECRETIONS 


227 


for red corpuscles which it will squeeze into the circulation in 
time of need. An English physiologist has shown that 
animals having spleens withstand poisoning by carbon mon¬ 
oxide gas more successfully than do animals without this 
organ. You will remember that carbon monoxide kills by 
tying up the hemoglobin of the blood in a useless compound. 
An animal breathing this gas can accordingly live longer if it 
can bring into service extra hemoglobin which has been stored 
in the spleen. 


Discussion 

1. Explain what is meant by internal secretions. 

2. Name the products of the pancreas. 

3. What is the effect of too little thyroid secretion? Of too 

much? 

4. What is the work of the secretion of the pituitary body? 

5. Under what conditions is adrenalin discharged into the blood? 

What is the result? 

6. Describe the physiological effect of fear, worry, or anger. 

7. Tell all you can of the function of the spleen. 


XVII 


THE BODY TEMPERATURE 

How does the human body keep the same temperature in sum¬ 
mer and winter? 

Do all animals do this? 

Does sweating make one warmer or cooler? 

What is fever? 

Those who live in the temperate zones are accustomed to 
extremes of heat and cold. In Boston, for instance, the ther¬ 
mometer has been known to drop to 13 degrees below zero 
and to rise to 103 degrees above. In some places the varia¬ 
tion is even greater. It is remarkable that we pass through 
these great changes in the weather without any decided effect 
on the temperature maintained in the interior of our bodies. 
Of course, the skin is warmed and cooled according to the 
condition of the air, but not far below the surface of the body 
a nearly constant standard is preserved. The temperature 
of the circulating blood cannot change more than a degree or 
two without signs of trouble. 

The production and loss of heat. — A thermometer with 
its bulb held under the tongue usually registers 98.6 degrees 
Fahrenheit. Since the outside temperature is seldom so high 
as this, it is plain that the body is most of the time warmer 
than its surroundings. We shall see that the reverse may be 
the case under some conditions. We must not forget that the 
active tissues are always producing heat. If the temperature 

228 


THE BODY TEMPERATURE 


229 


of the body is nearly constant, this must mean that heat is 
lost from the body at the same rate at which it is made by the 
activities within it. How is the balance between heat pro¬ 
duction and heat loss so successfully maintained? 

Most of the heat set free in the body has its origin in the 
muscles. It comes from the oxidation, or burning, of food. 
The blood circulation distributes this heat through the body. 
It escapes through the skin and by way of the breath. We 
easily understand how it may do this when the surroundings 
are cooler than the body itself, for the heat will then pass into 
the surrounding air and objects, making them warmer. 
But what happens when the temperature of the outside world 
is higher than that of the body? It would appear that the 
tendency would be reversed; that heat from the air, the floor, 
and the walls of the room would be absorbed by the body 
even while it still continued to produce heat within. 

To understand what happens you need to have a clear idea 
of the structure of the skin. In Chapter II you read that 
the cells of the outer skin are in many layers and that those 
nearest the surface are dry and dead. Deeper down, the cells 
are living and moist. Among them are nerve fibers. Still 
deeper is the inner skin, which is composed more of a fine 
network of connective tissue fibers than of cells. There is a 
good deal of fluid in the meshes of this network, and there are 
twisted loops of capillaries conducting blood. The amount 
of blood finding its way through this tissue varies greatly: the 
vessels dilate when the skin is heated; they contract when the 
skin is cooled. They can be made larger or smaller by the 
influence of the nervous system, even when the temperature 
of the skin does not change. 

The sweat glands have also been mentioned. Each one is a 


230 


PHYSIOLOGY AND HEALTH 



A PRIMITIVE WATER COOLER 

For centuries people in hot, dry climates used porous earthenware jugs 
for cooling water. This one was made in Spain. 

microscopic tube of epithelial cells. Most of it is in a curi¬ 
ous coil deep in the inner skin. A capillary net is wrapped 
closely about the coil and this arrangement makes possible 
the passage of water from the blood into the tube of the gland 
to form the sweat. Nerve fibers are connected with the se¬ 
creting cells of the glands. Each sweat gland has its own 







THE BODY TEMPERATURE 


231 

outlet, which we call a pore. Of course the total number is 
very great. 

Evaporation. — There is only one way in which the sys¬ 
tem can rid itself of heat when the surroundings have a tem¬ 
perature higher than its own; that is, by evaporating water. 
This process cools any surface from which the water is dis¬ 
appearing into the air. So, when the sweat evaporates from 
the skin, the temperature of the skin is lowered; the blood 
flowing through its vessels is cooled, and this blood, by mix¬ 
ing with that from other regions, lowers the temperature of 
the whole body. In the same manner the linings of the 
breathing passages are cooled as the breath passes over them 
picking up the vapor of water which they always provide. 

The principle of withdrawing heat by evaporation is used 
in the water coolers of tropical countries like Egypt. Water 
is placed in great jars of pottery so porous that there is a 
slow leakage through the walls. The water that comes 
through the walls of the jars evaporates rapidly into the hot 
dry air; thus the jars and their contents are kept compara¬ 
tively cool. Automobiles will be seen frequently in the hot, 
dry, semi-desert regions of the southwestern states with can¬ 
vas water bags swinging from them so that they will catch the 
breeze. Despite the fact that these bags often hang in the 
full glare of the sun, the water within them is cool and re¬ 
freshing. 

There is a limit to the amount of water which can be taken 
up by a given volume of air. We know that there are certain 
days when we feel the heat intensely, days which we call 
'sticky’ or 'muggy.’ We mean that there is so much mois¬ 
ture in the air that the latter does not readily absorb the 
sweat as it comes through the pores. The skin remains wet 


232 


PHYSIOLOGY AND HEALTH 


and grows uncomfortably warm. At such times it is likely 
that the temperature of the body as a whole goes up a little 
and we feel, quite correctly, that we ought not to be too active. 

Notice how a fan benefits the body in hot weather. It 
sends a current of air over the skin and this helps to remove 
heat, even when the temperature of the air is actually higher 
than that of the skin, because the faster evaporation cools the 
skin. When a man is running, he may be producing ten times 
as much heat as he would if he were resting; so it is a real prob¬ 
lem how to get rid of it. But in one way he is then fanning 
himself: as he moves through the air the effect is the same as 
though he were standing still and the air were passing over 
him. During exercise the warm moist air which has been 
inside the clothing and next to the skin is constantly worked 
out and replaced with cooler and drier air. Wearing little or 
very porous clothing aids this process of evaporation. 

A man can stand very high temperatures if only the air is 
dry. He can even stay for a few minutes in air so hot that it 
would set water boiling, because in such a place there is a very 
rapid evaporation of water from the skin and the air that is 
actually in contact with the body is not so hot as the air a few 
inches away. Men are able to do heavy work in the firerooms 
of steamers because the air, though intensely hot, is dry and 
in rapid motion from forced ventilation. You cannot tell by 
the appearance of the skin whether much sweat is being se¬ 
creted or not; so long as the water evaporates as fast as it 
reaches the pores, we fail to see it at all. We notice it only 
when it is secreted faster than it can be evaporated. This is 
the time when sweating is not benefiting us to the fullest ex¬ 
tent. 

We have seen that the body guards against being over- 


THE BODY TEMPERATURE 


233 


heated in hot weather by bringing a large share of the blood 
to the surface and by evaporating water as may be necessary. 
Many animals depend less on sweating and more on panting 
than human beings do. The dog cools his blood by making 
the air pass to and fro over his extended tongue, against the 
roof of his mouth and over the lining of his throat. He 
hardly sweats at all, but the evaporation of water from his 
mouth serves him in just the same way. 

Heat control in cold weather. — What happens when the 
weather grows cold? Less water is evaporated from the skin 
then, and, though more may be lost through the breath, there 
is, on the whole, a saving. We find that less blood comes 
into the skin, which naturally grows cool. Nature evidently 
undertakes to prevent too great a loss of heat through the 
surface of the body. When we put on extra clothing, we are 
taking another step in the same direction. Animals often 
do something like this by curling up or squatting so that they 
do not expose so much surface to be chilled. 

If we cannot combat cold entirely by reducing the loss of 
heat, we have to go to work to produce more. ‘Going to 
work’ is exactly what is meant, for it is the muscles which are 
used to produce the additional heat needed by the body to 
prevent its cooling off. We may shiver or we may begin to 
move about. In either case we exercise, and this always 
means that more heat is produced in the muscles and dis¬ 
tributed by the blood. 

It is a peculiar thing that the moisture in the air makes us 
feel the heat more in summer and the cold more in winter. 
We have seen that dry air in summer is less uncomfortable 
than damp air. People always agree that a dry cold climate 
does not make them so uncomfortable as one which is damp, 


234 


PHYSIOLOGY AND HEALTH 


though actually not so cold in degrees. Air which is both 
damp and cold takes heat more rapidly from the skin than 
does air which is cold but dry. 

Clothing. — Modern man uses many kinds of clothing. 
From animal sources he makes garments of wool and silk, fur 
coats, and leather jackets. From the vegetable kingdom he 
gets material for cotton and linen garments and for rubber 
coats. The effect of different kinds of garments upon the 
body temperature is determined by three factors: the rate at 
which they conduct heat, the readiness with which air passes 
through them, and their effect upon the evaporation of perspi¬ 
ration. A brief study of each of these characteristics will 
help us to understand the effect of different kinds of clothing 
upon the body. 

The warmth of clothing is due in part to the fact that it 
conducts heat slowly. A good example of this property is 
seen in the use of a cloth holder to handle hot dishes on the 
cook stove. A piece of metal which is too hot to touch with 
the hand can be held for a minute or two before the heat can 
make its way through the cloth holder. In a somewhat simi¬ 
lar way clothing retards the escape of heat from the body in 
cold weather. We can imagine how cold we should be in win¬ 
ter if we tried to dress in cloth made from weaving together 
very fine metal wires. Woolen cloth conducts heat least 
rapidly; silk more rapidly; cotton, linen, and rayon most 
rapidly. 

Perhaps even more important than the rate at which heat 
travels along the fibers of the cloth is the rate at which air 
passes through the fabric. This will be determined by the 
thickness of the material, the way in which the cloth is woven, 
and the number of layers. Cotton may be made into lace, a 


THE BODY TEMPERATURE 


235 


pair of thin cotton hose, or cotton-flannel pajamas. The 
nature of the fiber is the same in each case, but the difference 
in warmth depends upon the rate at which air passes through 
the cloth, and this in turn depends upon the nature of the 
weave. 

If cloth of the same thickness and the same kind of weave 
were made from wool, silk, cotton, and linen, we should find 
that the warmth of the garment would be in the order men¬ 
tioned, woolen being the warmest. We have seen that this 
would be the order in which they would be arranged in respect 
to their ability to conduct heat; it is also the order of arrange¬ 
ment in the capacity of the different materials to prevent cold 
air from reaching the skin quickly. 

Fur coats, leather jackets, rubber coats, and oilskins al¬ 
most completely prevent the passage of air. These outer gar¬ 
ments are very warm because they prevent the escape of the 
blanket of air which has been warmed by the body. 

The rate at which the evaporation of moisture takes place 
through different kinds of clothing is of importance only 
when we are perspiring or have accidentally gotten wet. 
Woolen cloth has the greatest ability to absorb water, although 
silk can absorb a considerable amount. Cotton and linen ab¬ 
sorb very little. A woolen garment takes longer than a cot¬ 
ton garment to dry; water evaporates more rapidly from 
the cotton. 

You may have noticed that you are colder after coming out 
of the water if you wear a cotton bathing suit than if you wear 
a woolen suit. If you lay a piece of wet cotton cloth over the 
back of one hand and fan it you will find that the hand feels 
much colder than when the same experiment is tried with a 
piece of wet woolen cloth. The thin cotton garments which 


PHYSIOLOGY AND HEALTH 


236 

we wear in the summer allow the perspiration to evaporate 
rapidly and this helps to keep us cool. For winter use, out¬ 
side coats which are made of fur or leather are warm and sat¬ 
isfactory unless we are so active as to perspire while wearing 
them. In this case the perspiration cannot escape and an 
occasional breath of cold air feels chilly. 

Clearly the problem in hygiene, so far as clothing is con¬ 
cerned, is that of dressing for the conditions which we are 
likely to encounter during the day. It is not difficult to know 
what is best to wear in hot weather, or in cold weather either, 
if one is to be out of doors continuously. The real difficulty 
arises for the person who lives in a cold climate but who 
spends much of his day in the summer temperatures of an 
office or living room. The facts which have just been pre¬ 
sented indicate that he will do best to wear cotton garments 
next to the skin and put on extra wraps when he goes out. 
If woolen garments or too many clothes are worn inside, the 
skin is kept too warm and it becomes unduly sensitive to the 
cold. Woolen undergarments absorb the moisture of per¬ 
spiration and become so damp that there is a chilling effect 
when the cold air strikes them. A cotton undergarment re¬ 
mains dry and keeps one comfortable during the day. We 
do not expect a great deal of warmth from it when we go out 
into the cold air, but we can get on very well when we are 
out of doors by wrapping up with outside garments or 
by exercising vigorously, thereby producing more heat with 
which to warm the body. We shall do well to avoid tight 
clothing of any kind because that interferes with the circula¬ 
tion of the blood. 

Bathing. — We bathe to be clean, to make ourselves ac¬ 
ceptable to others, and to maintain our self-respect. The 


THE BODY TEMPERATURE 


237 


health and comfort of the skin depend on its being clean. To 
keep it so, it is necessary to bathe and to have clean clothes. 
There is no need of dwelling on this point. There are, how¬ 
ever, some points to bring out in regard to the physiological 
effects of different types of baths upon the system as a 
whole. 

Baths are usually described as of three kinds: hot, indiffer¬ 
ent (or tepid), and cold. You know that the blood has a 
temperature of about 99° Fahrenheit. The skin is not so 
warm as this, generally speaking, but nearer to 90° for the 
parts covered by the clothing. The hands and face may be 
still cooler. Our judgments as to what is warm or cold are 
based on comparison with the skin; hence the water of a bath 
at 90° seems neutral; it neither heats nor cools the body. 
Such a bath answers for cleansing and ought not to interfere 
with digestion. But in the process of getting dry the skin is 
usually cooled, because the evaporation of moisture has the 
same effect as sweating. In this way one may become chilled 
even after a tepid bath if the room is cold and drafty or if 
the towel is not used with sufficient energy. 

A distinctly hot bath brings the blood to the surface and 
restores the feeling of warmth to one who has been chilled. 
It is more actively cleansing to the skin because the sweat 
glands are put to work and their-secretion washes the surface 
layers as it wells up through them. After a hot bath, how¬ 
ever, we are more sensitive to cold, and the contrast between 
the hot water and the ordinary temperature of the room is 
like that of exposure to cold air. For this reason the safest 
plan for taking a hot bath is to set the time in the evening 
and go directly to a warm bed. 

Cold baths should be short and followed by vigorous rub- 


PHYSIOLOGY AND HEALTH 


238 

bing. Unlike hot baths, they prepare one for activity, both 
mental and muscular, rather than for rest. If the glow 
does not follow cold bathing, the shock has been too severe. 
Some persons experience the glow, but later feel weak and 
chilly. A cold bath is of doubtful value to them. 

Swimming and bathing outdoors can often be enjoyed for 
a length of time which would be exhausting indoors because 
so much heat is produced by the muscular activity. 

Salt water is believed to have a particularly invigorating 
effect. Probably what happens is something like this: one 
comes from the beach with the surface layers of the skin 
soaked with sea water; then as the skin dries some salt is left 
among the cells. This salt attracts water from the deeper 
levels and the effect is pleasantly stimulating. After a while 
the extra salt will be removed by sweating and fresh-water 
bathing. 

The vasomotor system. — The wonderful adjustments 
which the body makes in order to maintain the same tempera¬ 
ture are controlled by the central nervous system. The sta¬ 
tion for this function seems to be in the brain, not in the 
highest part (cerebrum) but in one of the lower levels. From 
here are ordered the changes which determine how large a 
share of the blood shall circulate in the skin, how active the 
sweat glands shall be, and whether the muscles shall be called 
upon for extra supplies of heat. The changes may in part 
be reflexes due to the warming or cooling of the body surface, 
but they are known to be set up also by the variations in the 
temperature of the blood which reaches the brain. If the 
blood is too warm, its arrival in the brain sets up the exact 
changes which cool it; if it is too cool, its arrival sets up 
changes which will warm it. 


THE BODY TEMPERATURE 


0 


239 

Warm-blooded and cold-blooded animals. — Not all ani¬ 
mals maintain a fixed internal temperature. Reptiles, frogs, 
and fish are warmed or cooled with their sur¬ 
roundings. We generally call them 'cold¬ 
blooded’ animals because they usually have a 
temperature lower than our own. But what 
we really mean is that they have no fixed tem¬ 
perature; they take the temperature of their 
surroundings. Of course they must produce 
some heat, because they burn fuel, but the 
burning does not warm them much. 

Fever. — When the body temperature does 
vary, it is more common for it to rise than to 
fall. If it goes up two degrees or more, there 
are symptoms of fever. In many of the in¬ 
fectious diseases, such as measles, pneumonia, 
and typhoid, the fever is marked. The poison 
of the disease seems to affect the nervous sys¬ 
tem in such a way that a false standard for the 
body temperature is set up. It is as though 
some one tampered with the regulating device 
attached to a furnace and made the house too 
warm. In severe fever the mouth tempera¬ 
ture may go to 104° or 105° Fahrenheit. Still 
higher temperatures are sometimes recorded, 
but they are alarming and usually do not con¬ 
tinue long. When our tissues are heated far 
above the normal their protoplasm seems to be 
so injured as to cause death. 

It must not be supposed that the skin is always hot when 
there is a fever. Usually it is, but it may be cool and pale. 


Courtesy of Taylor In¬ 
strument Companies 

A CLINICAL 
THERMOMETER 








240 


PHYSIOLOGY AND HEALTH 


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THE BODY TEMPERATURE 


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This is the case when one has what is called a ‘chill.’ The pa¬ 
tient feels cold, but his feeling depends on the condition at 
the surface and does not tell the truth about the interior. 
During a chill the actual temperature of the blood and in¬ 
ternal organs is climbing higher and higher. The oxidation 
(burning of fuel) taking place in the muscles and glands is 
producing heat and it is not escaping as freely as usual be¬ 
cause of the reduced circulation in the skin; so the body as 
a whole becomes warmer and warmer while the sick man con¬ 
tinues to shiver and ask for more covering. 

When the temperature falls below normal, there is ordi¬ 
narily great weakness. Changes in this direction are not 
common. They may occur after a severe run of fever when 
the crisis, or high peak, has been passed. They may also 
follow long exposure to cold. 

Discussion 

1. What is the temperature of our bodies under normal con¬ 

ditions? 

2. Where does most of the heat set free in the body originate? 

3. By what means is the heat distributed over the body? 

4. In what way does heat escape from the body? 

5. Explain how the bodily temperature is kept constant 

(a) when the surroundings are cooler than the body it¬ 
self; (b) when the surroundings are warmer than the 

body. 

6. What is usually the condition of the skin on a hot, muggy 

day? Explain the reason for this. 

7. Why do we take a ride on a street car or in an automobile to 

cool off on a hot day? 

8. Under what conditions is it possible to stand high tempera¬ 

tures? 


242 


PHYSIOLOGY AND HEALTH 


9. Why is it cool beside a fountain? 

10. How is too great loss of heat prevented in winter? 

11. Explain the main difference between warm-blooded and cold¬ 

blooded animals. 

12. What does a rise in body temperature indicate ? 

13. Discuss the health practices related to clothing and ventila¬ 

tion. (See appendix.) 

14. Explain why fresh air, with its changing rate of movement 

and changing temperature, makes one feel more alert 
than warm still air. 

Experiments 

1. See if you can find the story of the men who perished in the 

“Black Hole of Calcutta.” Can you explain with the aid 
of this chapter the probable reason for their death? 

2. Wet two round spots of equal size on the blackboard. Fan 

one. Why does the one fanned dry faster? 

3. Find the range of temperature for your city or town. 

4. Collect pictures of dress in the three temperature belts 

(Frigid, Temperate, Torrid). What part does dress play 
in regulating body temperature? 

5. Determine which is the cooler, a wet towel or a dry towel 

each of which has been kept in the same room. Explain. 

6. Using a thermometer, compare the rate of cooling of water in 

a covered and an uncovered dish (effect of evaporation). 


XVIII 


MUSCULAR ACTIVITY 

What are the definite benefits of exercise? 

How does exercise affect the circulation? 

What are the advantages of proper body mechanics? 

What kinds of exercise do you like best? Why? 

Why is the proper mechanical use of the body important to the 
athlete? 

You have been told that the skeletal muscles make up about 
half the mass of the body. They use much more than half of 
the oxygen we consume, and they produce much more than 
half the carbon dioxide we expel in the breath. They are 
organs not only of movement but also of heat production. 
From every point of view they are of the greatest importance. 
We call them Voluntary muscles/ by which we mean that we 
are free to choose whether we shall use them or not. 

The importance of exercise. — Our ancestors had to do 
a large amount of hard physical work. For generations 
their bodies were fitted to this active life. The bodies which 
we inherit from them need to be exercised. When the muscles 
are used, other sets of organs are necessarily put to work 
at the same time. You can easily recognize that this is true 
of the heart. It must be active just in proportion as the 
muscles are employed. They must have extra oxygen at 
such a time — often eight or ten times as much as when they 


243 


244 


PHYSIOLOGY AND HEALTH 


are at rest — and the heart must send them enough blood 
to deliver this oxygen. As to the central nervous system, 
muscular exercise means something more than the use of the 
centers which govern the muscles at work. Other centers 
are made active at the same time, providing for the necessary 
changes in the distribution of the blood and calling the sweat 
glands into action. 

The sense organs are exercised whenever the muscles are 
used. The eyes have their part and it is a very important 
one in many sports. You must not forget that the muscles 
themselves are richly furnished with sense organs. Every 
contraction is registered by the return of impulses. There 
is a section of the ear, you recall, that is concerned with 
keeping the balance. This machinery is put to work when 
the body is in motion. 

Let us examine in more detail these effects of muscular ac¬ 
tivity on various systems. First, there is the effect on the 
muscles themselves. One of the first things a schoolboy is 
taught is that use makes his muscles grow. He is likely to 
think that this is the whole story of training. We cannot ex¬ 
plain just how use leads to growth, but we have other exam¬ 
ples of the same principle. You must bear in mind that the use 
of living organs means that something is spent or sacrificed. 
When a destructive process is under way, nature tends to 
make up for it by repairing the damage and often does this 
so generously that the result is actual growth. 

The formation of a callus in the skin is one illustration of 
this. When you first press down the strings of your ukulele 
you wear away the skin at the finger tips and find them be¬ 
coming tender. But soon the injury is more than made good: 
where the skin was worn thin, it has become unusually thick 


MUSCULAR ACTIVITY 


245 


and tough. The lost cells are replaced by new ones in much 
greater numbers. Here is another example. When one has 
a germ disease, the body may develop something to defend it¬ 
self against the poison which is disturbing it, an ‘antitoxin,’ 
as we say. In such a case the manufacture of antitoxin does 
not stop when just enough has been provided for the emer¬ 
gency; there is a liberal production of the protective agent, 
an extra supply. 

So when a muscle grows with exercise, the case seems simi¬ 
lar. In one respect such growth is different from that of a 
callus. The number of muscle fibers does not increase, but 
they become thicker individually. A trained muscle has a 
coarser grain than one which has had little use. No doubt 
one thing which favors the growth of an exercised muscle is 
the large supply of blood which it receives. We need to rec¬ 
ognize that quality in muscle is as important as size, probably 
more important. Big muscles usually mean great strength 
for momentary efforts, but they do not always mean great en¬ 
durance. You may know of women with small muscles who 
can keep on with house cleaning or work in the laundry for 
long hours. Slender girls can continue dancing for a long 
period. 

Probably one of the important gains with training is in¬ 
creased ability to bring all the fibers of muscles under the 
command of the nervous system. The fibers of skeletal 
muscle do not stimulate one another. Active and idle ones 
may be side by side. Every fiber which contracts does so 
because it receives impulses from headquarters. It is likely 
that an untrained man cannot get anything like a hundred 
per cent response from his muscle fibers. The power has to 
be secured by practice. As it comes, the subject finds that 


PHYSIOLOGY AND HEALTH 


246 

his strength is increasing much faster than the size of his 
muscles. 

Exercise, of course, develops skill as well as strength. 
This is related to the training of the nerve centers to give what 
we speak of as coordination. The changes which have to be 
made must be at every level from the spinal cord to the cortex 
of the cerebrum. When a new form of work is undertaken, 



Courtesy of Massachusetts Institute of Technology. 
THE START OE THE RACE 

Note the energy being used to get away from the mark. 

there is likely to be much wasted energy. A boy tries to ride 
a bicycle. He grips the handlebar so hard that his hands be¬ 
come lame. He puts many muscles under tension without 
any useful result. The foot that is coming up resists the 
foot that is going down. He quickly becomes heated and out 
of breath. A few weeks later the same boy rides with ease. 
He is no longer contracting muscles which do not help to drive 










MUSCULAR ACTIVITY 


247 

the wheel. There is no strife between the forces he exerts; 
each movement is promptly stopped at the right instant, and 
the next follows without delay. If the energy expended by 
the boy in his early practice were compared with that ex¬ 
pended in his skilled riding, we should find a great gain in 
economy. He now rides easily because his nervous system 
has become trained to direct the performance. He may have 
stronger muscles than before; but even if he has not, his de¬ 
velopment has advanced. 

Exercise and the heart. — The use of the skeletal muscles 
makes a demand on the heart. You know that this organ is 
itself a mass of muscle of a peculiar kind. We make it beat 
hard and fast when we set our other muscles to work. 
When we take exercise, the heart immediately responds. 
There are two reasons for this. In the first place the nerves 
which govern the heart are brought into play. You may re¬ 
member that there are two sets of these nerves and that we 
have likened them to the whip and reins used in managing a 
horse. The heart is usually under a certain restraint, but 
when the muscles are active this check is removed; the reins 
are slackened. At the same time the other sort of nerves 
excite the heart to greater efforts. 

As a result of experiments we know that, even if the nerves 
were disconnected, the heart would pass along more blood 
during exercise and would work harder in doing it. When a 
man who has been standing still begins to run, a large quan¬ 
tity of blood is thrust toward his heart along the course of the 
veins. The arrival of this extra blood opens the ventricles to 
a larger capacity and they gallantly undertake to keep their 
output equal to the inflow. Most physicians teach that the 
heart, like any other muscle, is made stronger by exercise. 


248 


PHYSIOLOGY AND HEALTH 


It can probably be overdeveloped, but this is not very com¬ 
mon. Unfortunately there are some hearts which are de¬ 
fective from the beginning. When this is the case, we need 
to know it and avoid strain. This is one reason why a careful 
examination of school children is important. 

A trained man has not only a strong heart but also an 
efficient vasomotor system. This means that his nerve cen¬ 
ters have power, to contract certain sets of blood vessels and 
open widely other sets to support his activities. You will 
remember that, when exercise is undertaken, more of the 
blood than before is directed to the muscles. Extra blood is at 
the same time sent to the skin, for the surplus heat which is 
being produced must be allowed to make its escape from the 
body. In order to have the necessary blood for the muscles 
and the skin, there is a reduced amount in the organs of the 
abdomen. The vessels in these organs are tightened under 
the influence of the governing cells in the central nervous sys¬ 
tem. You will see that, when you use the centers that control 
the skeletal muscles, you unconsciously exercise those that 
regulate the state of the blood vessels. 

This positive use of the vasomotor system certainly makes 
it better able to meet demands which may be made upon it. 
A condition of drowsiness is a sign of poor circulation in the 
brain and probably means that a large share of the blood is 
taking the path through the organs of digestion. We know 
that when we are sluggish and dull, a period of activity can 
make us feel more alert and alive. We can see what must 
have happened. The vessels of the abdomen have been con¬ 
tracted and the supply of blood to other parts, including the 
brain, has been much improved. One of the important char¬ 
acteristics of the man in good training — the man who is 


MUSCULAR ACTIVITY 


249 

fit — is the fine control which his nervous system maintains 
over the circulation. 

A well-developed vasomotor system has other uses besides 
that of giving effective support to the brain. It appears to 
be closely related to what we speak of as resistance. The 
hardy man recovers quickly from the strain of fatigue or ex¬ 
posure to cold. A most essential part of such recovery is the 
readjustment of the circulation. Two persons take cold 
baths — perhaps involuntarily by breaking through the 
ice. One of them is soon warm and comfortable again; 
his skin is in a glow, and he is none the worse for his experi¬ 
ence. The other does not rally so well. We say that he does 
not react after the shock to which he has been subjected. He 
continues to feel cold and miserable. His skin is pale or blu¬ 
ish. Very likely this turns out to be the beginning of an ill¬ 
ness. The main difference between these two persons is in 
the nature of their vasomotor systems, their capacity to re¬ 
store the circulation to normal after a disturbing influence. 
This capacity is generally associated with muscular fitness, 
and the lack of it with indolent living. 

Exercise and breathing. — Exercise always means in¬ 
creased breathing. Moderate activity means deepening of 
the movements, and greater effort brings increase of rate be¬ 
sides. We have already said that this mechanical use of the 
lungs is favorable to the health of their tissue. If a man is so 
lazy that he seldom gives himself occasion to breathe deeply, 
there will be parts of his lungs in which there is little stretch¬ 
ing of their substance or exchange of air. This is particularly 
true of the uppermost portions, the conical tips which come 
near the level of the collar bones. Tuberculosis is especially 
likely to begin in this locality. Strong and quick breathing 


250 


PHYSIOLOGY AND HEALTH 


movements are helpful to the circulation. The sharp con¬ 
tractions of the diaphragm push blood out of the abdominal 
veins and thrust it up toward the heart. So the effect of 
breathing in exercise is similar to that of the vasomotor 
changes; it works blood out of the abdominal organs and into 
other regions. 

Exercise and nutrition. — We have found it easy to show 
that exercise benefits the systems which carry on circulation 
and respiration. What can be said about nutrition? Here 
the story is not so simple. The first effect of exercise on di¬ 
gestion, if it is going on at the time, is probably not a favor¬ 
able one. The digestive organs are more or less robbed of 
blood. This means that the secretion of the juices may not 
be so well kept up. Teachers of hygiene recognize this fact 
and generally advise against much activity immediately after 
meals. When the work done is particularly hard and there 
is much sweating, constipation may result. Probably there 
has been so great a loss of water through the skin that there 
is not a sufficient surplus to flush the intestine. 

More moderate exercise is usually found to promote the 
success of digestion and the activity of the intestine. The 
mechanical effect of muscular movements on the mixture in 
the stomach and farther down the canal may be helpful. 
The walls of the tract are perhaps massaged in such a way as 
to assist in transporting absorbed food from the intestine to 
the liver or along the pathways of the lymphatic system. In 
many cases the best part of the reaction of exercise upon the 
body is the stimulation of appetite. After the digestive or¬ 
gans have had proper rest, the next meal is eaten with un¬ 
common relish. Food which is enjoyed is usually well di¬ 
gested, as you have been told before. 


MUSCULAR ACTIVITY 


251 


Exercise and the skin. — Many believe that periods of 
active sweating, such as accompany exercise, are decidedly 
beneficial. Sweating, when followed by bathing, leaves the 
skin clean through its entire thickness. This must be a de¬ 
fense against the entrance of the bacteria which are respon¬ 
sible for pimples and many other blemishes. Sweating leads 
to thirst and the drinking of water. In the course of an active 
day the amount of water taken into the intestine, absorbed 
into the blood, and passed out through the skin may be more 
than you would readily believe. Just consider that a football 
player may lose ten pounds in playing a single game. This 
loss is almost entirely water, and he will soon be led to drink 
as much more. There seems to be no doubt that the passage 
of so much water through the body leaves the system fresh¬ 
ened and benefited. 

Forms of exercise. — The best forms of exercise, generally 
speaking, are those which are interesting. We have said that 
the sense organs are trained to a greater degree in games than 
in simple calisthenics. If exercise is to do the most possible 
for developing an efficient brain as well as a strong body, it 
should be varied and give one new problems every moment 
rather than demand only mechanical repetitions of move¬ 
ments. Sports afford this variety and, what is extremely 
important, train one in team play and not simply in inde¬ 
pendent activities. They have a social as well as an indi¬ 
vidual value. Of course exercise out of doors is superior in 
many ways to that which is taken under cover. Sunlight is 
health-giving. It not only stimulates us through the eyes, 
making us alive to the beauty of the world, but its rays act 
with wholesome effect on the skin and apparently on the blood 
itself. This is a recent belief; only a few years ago we sup- 


252 


PHYSIOLOGY AND HEALTH 



Courtesy of the sculptor, Mr. Cyrus Dallin. 

THE FAMOUS STATUE OF MASSASOIT 

Note the erect head, the well-developed body and the strong abdominal 
muscles. What movement would the figure make to assume the stand¬ 
ing position which you are taught at school ? What change would this 
make in the lines of the body ? 


MUSCULAR ACTIVITY 


253 

posed that the benefits of sunlight were almost wholly con¬ 
nected with its tendency to make us cheerful. 

Even though we have said so much in favor of outdoor 
sports, we ought still to point out that class work in the gym¬ 
nasium has certain advantages. Many games have an un¬ 
equal effect on the development of the two sides of the body. 
Special exercises under the direction of an instructor may 
serve to correct one-sidedness and so be worth while, no mat¬ 
ter how dull they seem. Then, too, the matter of good pos¬ 
ture can be given the attention it deserves by a director of 
floor work, while it cannot have the attention of a coach in 
the games to any such extent. 

Posture. — By posture we mean the position in which the 
body is held in the sitting, standing, and lying positions. 
Each of these may be good or bad. You have heard the pre¬ 
cepts for good posture: abdomen flat, chest high, chin in, head 
erect. You have all seen boys and girls who carried their 
bodies well. Others do not seem to know what to do with 
their bodies. They stand in awkward, unsightly, Tag doll’ 
positions, letting the chest sag and the shoulders droop. Un¬ 
fortunate habitual positions may result from these careless 
attitudes or from fatigue, lack of rest, and the effects of 
improper diet. 

Incorrect postures are of two sorts. The first group in¬ 
cludes exaggeration of the natural physiological curves of the 
spine. These are three in number: a slight inward curve at 
the neck, an outward curve in the upper back, and a second 
inward curve in the lumbar, or low-back, region. Increase 
of the inward low-back curve is called lordosis. An ex¬ 
ample of an increase in the upper outward curve is seen in 
round shoulders. An increase of the normal curve of the 


254 


PHYSIOLOGY AND HEALTH 


! 


neck is seen in the person whose head is 
thrust forward like a turtle’s. These 
are three of the most common defects 
of posture. Any one of these condi¬ 
tions is likely to be accompanied by one 
or more of the others, because the body 
is so constructed that if one part of the 
backbone is pushed forward, another 
part must curve backward in order to 
keep the balance. 

The second group of poor postures 
has to do with sidewise curvatures. 
Instead of being straight, with one 
vertebra directly over the next, the 
spine is curved to one side or to the 
other. Such a curvature may be a 
single slight swing of the spine to right 
or left, or it may be compound, that is, 
curved to the left at one place and to 
the right at another. This latter type 
is not common and usually develops 
following some illness, such as infantile 
paralysis, in which certain muscles may 
lose their strength and allow others to 
pull the spine out of shape. 

You have already learned that the 
muscles of the body consist, for the most 
part, of groups which pull in opposite 
directions. There is always a slight contraction in these op¬ 
posing groups which is called muscle tone. The very process 
of standing is an illustration of how muscle tone operates. A 







MUSCULAR ACTIVITY 


255 

few fibers of the muscles are always working. When the body 
swings far forward or backward, additional fibers of the op¬ 
posing group come into play and bring it back to the upright 
position. Sustained tone produces fatigue. Rest, however, 
should come through complete relaxation, not by slumping 
into poor posture. 

Poor posture is the result of a lack of balance between two 
opposing muscle groups in 
which one group has been 
pulling unduly hard, thus 
stretching out the opposing 
group. In the round-shoul¬ 
dered individual the muscles 
which draw the arms toward 
the chest have tightened 
through habitual contraction. 

Correspondingly, the muscles 
which draw the shoulder 
blades together will have 
been stretched. In order to 
correct such difficulties and 
make it possible to carry the 
body well, you will need 
special exercises which stretch the tight muscles and 
strengthen the weak ones. 

For the person who does not need special corrective exer¬ 
cises, good posture involves two things: first, strong muscles; 
and second, the will to use them. Strong muscles are de¬ 
veloped through exercise, sleep, and proper diet. To use 
them in keeping the body erect requires will power. Make 
sure that you know the meaning and the feeling of good 



This shows the lateral curving of 
the spine which may result from 
sitting in a poor writing position. 
























PHYSIOLOGY AND HEALTH 


256 

posture. Then practice taking your best position a few 
minutes each day. There are many times when you can do 
this. Walking to and from school is a good time to pull in 
the abdomen, lift the chest high, and swing along freely. 

The main point to remember in keeping good sitting posture 
is to use the trunk as a single unit and to lean backward or 
forward from the hips. Keep your chest high and your 
head erect. 

The benefits of good posture are not only physiological but 
also mental and social. The boy who holds himself alert and 
in readiness for every changing situation is more likely to be 
chosen for a big job. The knowledge that he is holding him¬ 
self correctly makes him at ease among his fellows and gives 
him a sense of power. If, in dramatics, you undertake to 
impersonate a successful man or an unsuccessful man, an 
honest man or a dishonest man, a courageous man or a cow¬ 
ard, a strong or a weak man, you will see how closely you as¬ 
sociate posture with character and ability. 

From the physiological standpoint there are several rea¬ 
sons for holding the body erect. The bones of the trunk pro¬ 
vide a framework in which the many sensitive and important 
organs perform their work. Each can do its work best if it is 
not crowded and pushed by the others. When you lift your 
chest, you can feel that you have more room for air. Try 
taking a deep breath with your chest slumped. You feel that 
you are pushing against an obstacle. Now enjoy the freedom 
of a deep breath with your chest lifted. 

The diaphragm, of which you learned in the chapter on 
Breathing, performs its function more efficiently when it has 
room to make its complete excursion up and down. It is 
possible to measure this excursion, and it has been found that 


MUSCULAR ACTIVITY 


2 57 


the diaphragm may move a very slight distance or it may rise 
and fall more than an inch. Some one has said that we sigh in 
order to give the diaphragm a chance to make its complete 
trip. 

When the organs of the abdominal cavity sag, or press 
against each other, a condition is established which may lead 
to illness in middle life, because the ill effects of poor posture 
tend to increase. The present effect of a poor bodily carriage 
is unnecessary fatigue; the future effect may be damaged 
organs. 

The muscles and ligaments also work at a disadvantage 
when the body is held in poor posture. A muscle may be so 
stretched and pulled out of position that it cannot perform 
its function promptly or forcefully. Strain may accompany 
its attempted contraction. In many colleges a freshman is 
not allowed to compete in athletics until he has learned the 
proper mechanical use of his body, even if he has been a star 
in the high school. The coach knows that poor body me¬ 
chanics means trouble sometime. 

The incorrect use of one part of the body may directly 
affect another part. An illustration of this is a strain at the 
knee, which often arises from a fallen foot arch. The per¬ 
sistent nagging pain which develops in the inner side of the 
knee cannot be effectively relieved by local treatment but is 
entirely done away with by strengthening or supporting the 
arch of the foot. 

The feet. — The human foot is obliged to meet very severe 
demands. It has to bear the whole weight of the body when 
one is taking a step and half this weight when one is standing 
still. It is intended to guard against shocks and jars. Hence 
it needs to be both strong and elastic. These properties are 


PHYSIOLOGY AND HEALTH 


258 


secured partly by the arrangement of the bones and ligaments 
and partly by the active contraction of muscles. Feet often 
fail to stand the strain put upon them 
and then they give trouble. 

You have heard of the condition 
known as ‘flat foot/ Since this is a 
faulty condition, the expression sug¬ 
gests that the normal foot is not flat. 
It is, in fact, arched. When a man 
is standing, his weight bears upon the 
keystone of the arch, the two ends of 
which are the heel and the ball of the 
foot. The toes should share the 
weight with the ball. Besides being 
arched from the heel to the toes, the 
bones of the foot are slightly arched 
from side to side in the region just 
behind the toes. The ligaments 
which bind the bones together tend 
to hold them in the arched arrange¬ 
ment. However, this is elastic. 
When you jump up and come down 
the arches of the feet flatten slightly 
and then spring up again. The 
arches are shock absorbers. 

The ligaments between the heel 
and the toes have been compared 
with the bowstring which holds the bow bent to a certain 
curvature. There are muscles running between the same 
points; if they are relaxed, all the strain is on the ligaments; 
when they are in contraction, they share the tension and 



THE EOOT AND ITS 
SHOE 

A, the outline of the 
shoe; B, the outline of the 
foot; C, the footprint. 






MUSCULAR ACTIVITY 


259 




THE EFFECT OF HIGH HEELS 

The X-ray shows how the bones of the foot are distorted when the foot 
is forced into a poorly shaped shoe. 

there is less tendency to stretch the ligaments beyond the 
length it is best for them to have. Overweight is, of course, 
hard on the feet. 








260 


PHYSIOLOGY AND HEALTH 


To keep the arches from sagging, it is of chief importance 
to bend the toes vigorously when walking. Little children 
and most persons who go barefoot have this habit. Wearing 
stiff shoes is likely to cause us to discontinue this good prac¬ 
tice. If we cease to make this effort we are likely to weaken 
the bowstring just mentioned. You may find it tiresome to 
walk in soft, flexible shoes. A moderate amount of such 
walking is a fine thing for the muscles. Those who know 
most about the hygiene of the feet tell us that the toes should 
be pointed straight ahead and the heels not swung inward at 
each step as is a common practice. Shoes should be porous 
to avoid overheating the feet and keeping in the moisture. 
They should be roomy, especially to give freedom of move¬ 
ment to the toes. The most common fault with shoes is a 
shape which causes them to press the great toes toward the 
other toes; this greatly lessens the elastic spring of the feet 
and may cause trouble at the joint of the great toe. 

Discussion 

1. What evidences can you give for the importance of exercise? 

2. Explain how the heart meets the demands of muscular ac¬ 

tivity. 

3. How is the health of the lungs improved by exercise? 

4. Explain what happens in the skin during vigorous exercise. 

5. Discuss the health value of different kinds of exercise. 

6. Describe the common faults of posture. 

7. What is muscle tone? 

8. What are the conditions of good standing and sitting pos¬ 

ture? 

9. Discuss the immediate and possible future ill effects of poor 

posture. 


MUSCULAR ACTIVITY 


261 


10. Describe the structure and function of the foot. 

11. What are the two arches of the foot? 

12. Discuss the health practices related to posture, the skin, and 

the feet (see appendix). 


Experiments 

1. Record your footprint at home by wetting the sole of the 

foot and stepping on a clean piece of paper. Outline the 
print with a pencil before the paper dries. Bring the print 
to school. What does it suggest? 

2. Hop off the floor, landing on the toes. Try landing on the 

heels. What has this shown concerning the function of 
the foot? 

3. Demonstrate the muscles which pull the head forward and 

those which pull it backward. Do the same with the 
muscles of the shoulders. 

4. Demonstrate the posture used by persons engaged in differ¬ 

ent occupations and sports. Discuss each position. 

5. Let different pupils demonstrate correct sitting, standing, and 

walking postures. 

6. See how many times you breathe per minute. Run twenty- 

five or thirty yards at top speed. What is the breathing 
rate now? How long is it before the rate of breathing re¬ 
turns to normal? 

7. Collect information concerning loss of weight during a vigor¬ 

ous game either from your own experience or from records 
of athletes. 

8. With the help of your physical education teacher demon¬ 

strate exercises which might be used to correct round 
shoulders, hollow chest, turtle head, debutante slouch. 


APPENDIX 


This Appendix suggests some procedures which have been 
found useful in junior high schools. 

WEIGHING AND MEASURING 

All weighing and measuring should be done carefully and 
accurately. Weighing should be done once a month — if 
possible, always at about the same time of day. Height should 
be taken at least twice during the school year — at the begin¬ 
ning and in January or February. It is desirable that the 
student be weighed and measured without shoes. 

Weighing. — Before weighing, the scales should be tested 
for balance by pushing the balance weights back to zero. 
When the scales are found to vary somewhat from an accurate 
balance, they should be adjusted by the Sealer of Weights and 
Measures or by the teacher. If the scales are moved from one 
room to another, care should be taken to keep the platform 
relatively horizontal, so that the adjustment of the mechanism 
under the platform is not disturbed. The student being 
weighed should stand quietly in the middle of the platform with 
his hands at his sides. 

Measuring. — Two instruments are necessary for measur¬ 
ing: (i) an accurate scale against which the person will stand 
to be measured; and ( 2 ) a leveling device which can be placed 
on his head to secure a right-angle measurement against the 
scale. 

One of the best measuring scales is made of inextensible and 
unshrinkable paper, which may be tacked or pasted to a wall 

262 


APPENDIX 


263 

or specially prepared board. It can be secured from the 
American Child Health Association, 370 Seventh Avenue, 
New York City. You may use yardsticks fastened one above 
another on a smooth wall, or a tape measure tacked to the 
wall. Be careful to have them accurately placed. Such a 
scale should be checked by a standard steel tape. 

The leveling device may be made of two pieces of seasoned 
walnut board about seven by five inches. On the inside of the 
median line is a narrow strip with an opening which serves as 
a handle. If such a measuring device cannot be secured con¬ 
veniently, a box with a square edge may be used. (A chalk 
box serves the purpose very well.) The flat surface of a book 
or board cannot be used accurately, because one cannot be 
sure that it will always make a right angle with the scale on 
the wall. 

The person being measured should stand as tall as possible, 
with heels together and with his back and head against the 
wall where the scale is placed. His arms should be at his side, 
and his eyes straight ahead. 

Records. — It is well to keep two sets of records — one on a 
classroom weight-record sheet and another on individual weight 
cards. A regular form of “ Classroom Weight Record ” can 
be secured from the Bureau of Education, Department of the 
Interior, Washington, D.C. The classroom record should be 
kept hanging where students can refer to it — in the home 
room, the hygiene classroom, or the gymnasium. The indi¬ 
vidual cards may be carried home at regular periods to be 
signed by the parent. Both records should give height, weight, 
and average weight for height and age. 

It is desirable that junior high school students should have as 
large a share as possible in the weighing and measuring ac- 


264 


PHYSIOLOGY AND HEALTH 


CLASSROOM WEIGHT RECORD 



tivities. Certain ones can be trained to do the weighing, others 
to do the measuring. Each student can estimate the average 
for his height and age, and take part in keeping his own records, 
recording the figures on his own card or on the classroom weight 
record at the time he is weighed. It will be necessary for the 
teacher to supervise these activities. 

Importance of weighing. — It is desirable that one should be 
within the zone of normal weight — between 10 per cent below 
average and 20 per cent above. (See Weight-Height-Age 
tables at end of Appendix.) It is more important, however, 
that one should be growing regularly than that one should 
conform exactly to average weight for his height and age. Boys 
and girls of junior high school age should gain from one-half 
to one pound per month. 























































APPENDIX 


265 


After being weighed, each student should know his actual 
weight and how much he gained or lost. He should be expected 
to have an intelligent understanding of the relation of his 
health habits to his gain or loss in weight. Failure to gain for 
a month or two is not a serious matter, but the student who 
fails to gain should consider his daily habits carefully and cor¬ 
rect those which are faulty. If he fails to gain over a period of 
three months or more, he should receive individual attention. 

DIRECTIONS FOR MAKING A WEIGHT GRAPH 

Use paper which is already u squared ” for graphs, or rule a 
sheet of drawing paper for the purpose. The horizontal lines 
will represent “ pounds of weight.” The vertical lines will 
represent the “ months ” or the times at which weighings are 
made. 

Each horizontal line should be marked with a figure to show 
the number of pounds, but the numbers will be different for 
each student because the weights are different. Answer these 
questions before you plan your graph: What is your actual 
weight for the first month which you are recording on your 
graph? What is the average weight for your height and age 
at that time? Are you overweight or underweight? 

If you are underweight , let the fifth horizontal line from the 
foot of the graph be marked with the number of pounds which 
represents your actual weight. Each horizontal line below 
should be marked one pound lower and each line above should 
be marked one pound higher. 

If you are overweight, let the fifth horizontal line from the 
foot of the graph be marked with the number of pounds which 
represents the average weight for your height and age. Mark 
your lines above and below as directed. 


266 


PHYSIOLOGY AND HEALTH 


The vertical lines should be marked with the names of the 
months. On these lines dots are placed to indicate weight at 
weighing periods. The solid black line drawn between these 

dots makes a weight line, which 
falls when you are losing weight 
and rises when you are gaining. 

You can draw a light pencil 
line to represent your expected 
gain if you wish. Find out how 
much a student of your age 
should gain each month, and 
draw from the first dot, which 
represents your actual weight, 
a line which will show the ex¬ 
pected gain per month. 

At the time of your first 
weighing you should be meas¬ 
ured and learn the average 
weight for your height and age. 
The average weight on your 
graph may be represented in 
red. Place a red dot on the 












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WEIGHT GRAPH OF A GIRL 
WHO CAME UP TO WEIGHT 


proper month line to indicate the average weight for your 
height and age. If you wish to draw a line from this across 
the graph, you may draw it on the basis of your expected 
gain per month, just as you drew your line of expected gain 
from the dot which showed your actual weight. You may 
prefer to postpone drawing a line of average weight until 
you are measured again and find your average weight for 
the new height. You can then locate a second red dot on the 
chart, and draw a line connecting the two. 



































































APPENDIX 


267 


PHYSICAL ACCOMPLISHMENT 

Your physical activities program contributes to the mainte¬ 
nance and development of health and it also serves as one 
measure of health. In the gymnasium, on the playground, 
or in sports you have an opportunity to demonstrate your 
ability in various ways and a chance to watch your improve¬ 
ment in physical accomplishment. In some schools it is 
possible for all pupils to determine their physical accomplish¬ 
ment in a definite set of stunts and activities. Their progress 
and improvement during the year are recorded. Whatever the 
nature of the physical activities program in your school may 
be, you will do well to regard your accomplishment in these 
activities as a means of health development and as one measure 
of health progress. Records of physical accomplishment may 
well be discussed in class. 

MAINTAINING HEALTH PRACTICES 

During the earlier years of school life you have carried on a 
training program in health through which you have developed 
proper health habits. You will want to be sure that these 
valuable practices are not discontinued in the rush of the 
increasing number of activities at home and at school. You 
may desire some organization of the homeroom or hygiene 
class through which health habits may be checked from time to 
time by means of inspection, questionnaires, and habit 
records. Plans for these activities may be developed by 
the class itself. You may wish to use the accompanying 
health score card and list of health practices in this connec¬ 
tion. 


268 


PHYSIOLOGY AND HEALTH 


HEALTH SCORE CARD FOR BOYS AND GIRLS IN JUNIOR 

HIGH SCHOOL 


I. Signs of Health 


Score 


1. Can you work and play without being more 
than naturally tired at bedtime? 

2. Are you rested when you get up in the 
morning? 

3. Is your appetite for wholesome food good? 

4. Is your weight within 10 per cent below or 20 
per cent above average for your height and 
age? 

5. Have you gained the expected amount for your 

age since-? 

(Let teacher decide period of time.) 

6. Is your posture good? 

7. Are your feet strong and free from any defect? 

8. Are your muscles strong and firm? 

9. Is your vision either normal or corrected by 
glasses? 

10. Can you hear ordinary conversation at sixteen 
feet? 

11. Is your skin clear? Color good? 

12. Is your hair glossy, but free from excessive oil? 

13. Are your teeth either sound or filled? 

14. Are you free from constantly recurring illness, 
including colds? 

15. Are your nose and throat free from defects, or 
treated in accordance with medical advice? 


Score 


II. Health Practices 

1. Do you drink at least two glasses of milk every 
day? 

2. Do you eat fruit at least once a day? 

3. Do you eat at least one vegetable, other than 
potato, every day? 

4. Do you eat an uncooked vegetable at least three 
times a week? 

5. Do you eat some dark bread every day? 

6. Do you drink at least six glasses of water every 
day? 

7. Do you refrain from using tea and coffee? 

8. Do you eat sweets in moderation and only at the 
end of a meal? 












APPENDIX 


269 


9. Do you eat only at mealtime? (Fruit and milk 
may be excepted.) 

10. Do you eat your meals at a regular time each 
day? 

11. Do you eat slowly and chew your food well? 

12. Do you eat a good breakfast, with either cereal 
or egg as a basis? 

13. Do you have a daily scrub with warm water and 
soap, including at least face, neck, ears, hands 
and arms, and wash your hands regularly before 
meals? 

14. Do you have a daily tonic bath with cold water 
in the morning (either shower, tub, or splashing 
on face, throat, and chest) or a dry rub with 
a rough towel? 

15. Do you take a full warm bath at least twice a 
week? 

16. Do you brush your teeth and gums at least 
twice a day? 

17. Do you clean your finger nails every day and re¬ 
frain from biting them? 

18. Do you average at least ten hours of sleep every 
night? 

19. Do you have a window open? 

20. Do you average at least two hours of outdoor 
exercise every day? 

21. Do you have a bowel movement every day? 

22. Do you try to maintain your best standing and 
sitting posture? 

23. For school and work do you wear shoes with 
low, broad heels? 

24. Do you remove outdoor clothing when you are 
indoors — heavy sweaters, suede jackets, rub¬ 
bers, overshoes? 

25. Do you have a complete physical examination 
by a physician once a year? 

26. Do you have your teeth examined and treated 
by your dentist at least once a year? 

27. Have you been vaccinated? 

28. Have you been immunized against diphtheria? 
(Negative Schick Test is O.K.) 

Score 

Total Score 


Score 

20 

20 

20 

20 

10 

10 

10 

10 

10 

30 

20 

30 

30 

20 

10 

10 

50 

40 

20 

20 

550 

1000 











270 


PHYSIOLOGY AND HEALTH 


HEALTH EDUCATION IN RELATION TO OTHER 
SUBJECTS 

Health is such a far-reaching factor in life that the student 
finds throughout many of his subjects an opportunity to 
broaden his health knowledge. Notice how the history of 
different peoples is associated with health. In geography, 
observe how climatic conditions and natural resources affect 
habits of living, customs, and industries. Social science, or 
civics, emphasizes constantly the importance of personal and 
community health as a prime factor in community life. 

General science gives you basic knowledge. The physical- 
education program contributes directly to the health of the 
students. Is each student profiting to the utmost by taking 
part in all those activities for which he is qualified? You 
should regard your ability in physical education as one measure 
of good development and health. 

Home economics is another subject which directly teaches 
health. Girl students should be appreciative of the opportu¬ 
nity to learn scientific facts about diet and care of the home. 
Is there any chance for boys to be instructed in a knowledge of 
foods and cooking which will aid them in camping? 

HEALTH HABIT OBJECTIVES 

The following list of health habit objectives is adapted from 
the Cleveland Tentative Health Education Program for Junior 
High School. 

Growth and 1. To determine one’s weight regularly. 

Health 2. To plan .a health-training program of the essential daily 

health habits. 

3. To live within one’s own physical limitations. 


APPENDIX 


Mouth and 
Teeth 


Posture 

Food and 
Habits of 
Eating 


271 

4. To brush the teeth at least twice daily in an approved 
way. 

5. To brush the gums and tongue properly. 

6. To use a toothbrush of the proper size, shape, and 
stiffness. 

7. To use one’s own toothbrush. 

8. To care for the toothbrush properly. (Rinse thoroughly 
in hot water.) 

9. To refrain from biting hard objects. 

10. To keep all foreign objects out of the mouth (pencils, 
fingers, money, etc.) (See also, Hands) 

11. To refrain from picking the teeth with pins. 

12. To select a diet rich in tooth-building material. 

13. To visit a dentist twice a year. 

14. To refrain from kissing any one on the mouth. 

15. To hold the body in an erect position when standing, 
walking, or sitting. 

16. To acquire a taste for milk, green vegetables, hard dark 
breads, and whole-grain cereals. 

17. To refrain from eating an excess of food. 

18. To include sufficient bulky food in the diet. 

19. To include sufficient hard food in the diet. 

20. To avoid sweets or to eat them rarely and never except 
at the end of a meal. 

21. To limit the amount of protein in the diet. 

22. To choose the most healthful meats. 

£3. To avoid eating fried foods. 

24. To avoid food fads (hot-water fad, no-breakfast fad, 
raw-food fad). 

25. To eat a simple warm lunch daily. 

26. To use iodized salt at home (if you live in a goiterous 
district). 

27. To eat a good breakfast each morning. 

28. To refrain from eating between meals, especially heavy 
foods and sweets. 

29. To take the heavy meal at the most healthful time of 
day. 

30. To avoid eating when hurried or excited. 

31. To eat three regular meals a day. 


272 


PHYSIOLOGY AND HEALTH 


32. To drink plenty of water between meals. 

33. To avoid ice water or drink only small portions. 

34. To drink a glass of water before breakfast. 

35. To use individual cups. 

36. To use drinking fountain properly. (See also, Sanitation) 

37. To drink slowly. 

38. To refrain from using soft drinks, except at meals and 
then rarely. 

39. To take small bites and mouthfuls. 

40. To eat slowly and to chew food well. 

41. To refrain from drinking while food is in the mouth. 

42. To rest before and after eating when possible. (See also. 
Rest) 

43. To sit properly at the table. 

44. To be calm, cheerful, and polite at the table. 

45. To refrain from talking while food is in the mouth. 

46. To wash hands before handling food or eating. (See 
also, Hands) 

47. To refrain from exchanging food or from eating food 
picked up from the floor, ground, or street. 

48. To wash or peel fruit before eating it. 

49. To wash dishes properly after using them. 

50. To use one’s own napkin. 

51. To refrain from handling other people’s food. 

52. To protect food from dust, flies, and rodents. 

53. To handle and store fresh and prepared food properly. 

54. To evacuate the bowels at least once daily at a regular 
time, preferably just after breakfast. 

55. To take sufficient water to aid digestion and elimination. 

56. To take sufficient bulky food to aid elimination. (See 
also, Food) 

57. To take sufficient active exercise each day as an aid to 
elimination. 

58. To use toilets and lavatories in a sanitary way. 

59. To avoid the abuse of cathartics. 


Elimination of 
Body Waste 


Skin 60. To take a cleansing bath at least twice a week, prefer¬ 

ably daily. 

61. To wash the face, neck, and ears daily with warm water 
and soap. 


APPENDIX 


273 


Hands 


Hair 


Fresh Air , 
Ventilation, 
and Sunshine 


62. To rinse and dry the skin thoroughly. 

63. To use one’s own towel and wash cloth and keep them 
clean. 

64. To provide skin stimulation in the form of cold bath, 
showers, or cold water on face, neck, and chest, followed 
by a brisk rub, or a dry rub with a rough towel. 

65. To care for roughness of the skin and chafing due to 
unavoidable exposure. 

66. To wash hands before eating or handling food. (See 
also, Food) 

67. To wash hands after using toilet. 

68. To keep nails short and clean. 

69. To refrain from biting nails or picking hangnails. 

70. To refrain from putting fingers into the mouth. (See 
also, Mouth ) 

71. To prevent or care for hangnails. 

72. To keep one’s hands clean when giving first aid. 

73. To use one’s own manicure articles. 

74. To brush and comb the hair daily. 

75. To use one’s own comb and brush and to keep them 
clean. 

76. To have the hair washed at least once in two weeks. 

77. To dry the hair thoroughly before going out. 

78. To massage the scalp by brisk brushing or rubbing. 

79. To keep the hair trimmed or tied so that it does not 
hang in the eyes. 

80. To prevent dandruff. 

81. To prevent pediculosis. 

82. To avoid useless and harmful tonics. 

83. To sleep with windows open at top and bottom. 

84. To maintain proper ventilation in rooms over which 
one has control. 

85. To avoid breathing dry, dusty air. 

86. To avoid breathing fumes. 

87. To avoid overcrowded and poorly ventilated places. 

88 . To breathe properly with mouth closed and abdomen 
contracted. 


274 


PHYSIOLOGY AND HEALTH 


Nose 


Disease 


Sanitation 


89. To get abundant sunshine into the home. 

90. To expose the skin to sunlight (to become tanned but 
not burned). 

91. To work and study in well-ventilated rooms. 

92. To choose outdoor recreation when possible. 

93. To breathe through the nose with the mouth closed. 

94. To blow the nose gently, one nostril at a time. 

95. To use only one’s own handkerchief. 

96. To use a clean handkerchief. 

97. To avoid picking the nose. 

98. To cover coughs and sneezes with a clean handkerchief. 

99. To obey quarantine regulations. 

100. To submit to vaccination against smallpox, typhoid 
fever, and diphtheria. 

101. To keep away from those who are ill with communi¬ 
cable diseases. 

102. To prevent colds. 

103. To treat colds properly. 

104. To be careful during convalescence. 

105. To practice those health habits which will protect 
against tuberculosis infection. 

106. To prevent the spread of skin diseases and infections. 

107. To help keep the schoolroom clean. 

108. To keep work material clean. 

109. To keep one’s desk, shelves, and drawers clean. 

no. To help keep the school grounds, home yards, streets, 
alleys, and also parks and camp sites, clean, 
in. To help maintain sanitary conditions of school and 
other public toilets. 

112. To maintain sanitary conditions of kitchen, bath, and 
bedroom. 

113. To have screen doors shut. 

114. To dispose of household waste and garbage, using 
proper receptacles. 

115. To use the drinking fountain properly. (See also, Food) 

116. To use the telephone properly. 

117. To handle money properly. 

118. To help to prevent the breeding of flies and mosquitoes. 


Harmful Sub¬ 
stances 


Sleep and Rest 


Clothing 


APPENDIX 275 

119. To refrain from drinking tea and coffee during the 
growth of the body. 

120. To refrain from drinking alcoholic beverages. 

121. To refrain from using any form of tobacco. 

122. To take medicine only according to the doctor’s in¬ 
struction (home remedies excepted). 

123. To have a regular bedtime. 

124. To sleep outdoors or with windows open. 

125. To sleep without artificial light in the room. 

126. To take a relaxed position for sleeping or resting. 

127. To use a low pillow or no pillow. 

128. To use sufficient light warm cover but not too much. 

129. To relax during rest periods at school or at home. 

130. To provide for sufficient rest and relaxation during the 
day. 

131. To rest after eating when possible. (See also, Food) 

132. To eat only light meals before sleeping. 

133. To avoid intense mental activity or excitement just 
before retiring (to have a quiet evening). 

134. To air bed clothing each morning. 

135. To confine parties to one week-end night. 

136. To sleep alone in one’s own bed and in one’s own room 
if possible. 

137. To remove clothing at night. 

138. To sleep in hygienic night clothing. 

139. To change sheets and pillow slips each week. 

140. To choose clothing of suitable size and style, suspended 
from the shoulders. 

141. To have clothing suitably adjusted for comfort and 
vigorous activities (no restraining bands or elastics). 

142. To keep clothing as clean as possible. 

143. To keep shoes clean and polished. 

144. To have clean underclothing and stockings at least 
twice a week (preferably oftener). 

145. To refrain from getting clothing wet if possible, and to 
remove damp clothing as soon as possible and warm 
the body if it has been chilled. 

146. To adjust the amount of clothing worn to the temper¬ 
ature and the weather. 




276 


PHYSIOLOGY AND HEALTH 


Feet 


Eyes 


147. To remove extra wraps, sweaters, and rubbers when in¬ 
doors. 

148. To avoid waterproofed material for constant wear. 

149. To wear underclothing suitable to climate and season. 

150. To avoid excessive neckwear and furs. 

151. To put on extra wraps when one is warm after exercise. 

152. To keep wraps and clothing neatly and in a proper 
place. 

153. To remove all clothing at night, spread it to air, and 
put on night clothes. 

154. To select hats that are ventilated and not too tight. 

155. To wear light-colored clothing during the summer. 

156. To wash feet regularly. 

157. To keep the nails short and clean. 

158. To prevent ingrowing toe nails by trimming them 
squarely, scraping thin on top, and wearing proper 
shoes. 

1591. To wear stockings of proper size. 

160. To wear shoes of proper size and shape (straight inner 
edge and low, flat heel). 

161. To wear rubbers at appropriate times. 

162. To remove overshoes indoors. 

163. To read only in proper light. 

164. To hold book or handwork in correct position and at 
proper distance from eyes. 

165. To avoid casting a shadow upon one’s writing or hand¬ 
work. 

166. To refrain from looking directly at the sun or extremely 
bright lights (wear eye shade when necessary). 

167. To avoid glare. 

168. To wear dark glasses when glare is unavoidable. 

169. To avoid excess of fine work. 

170. To rest the eyes frequently or when tired by closing 
them or focusing them on distant objects. 

171. To avoid reading while lying down. 

172. To avoid reading on moving cars. 

173. To avoid sitting too close to the screen at the movies. 

174. To avoid reading fine print, blurred letters, etc. 


Ears 


Safety 


APPENDIX 277 

175. To secure properly fitted glasses when necessary and to 
wear them according to the oculist’s directions. 

176. To have a periodic examination of one’s eyes. 

177. To keep frames of glasses properly adjusted (not bent). 

178. To keep the lenses clean. 

179. To refrain from rubbing the eyes, and to keep inap¬ 
propriate articles away from them. 

180. To remove properly any foreign objects from the eyes. 

181. To secure medical advice when there is trouble with 
the eyes. 

182. To bathe the eyes when they are sore or tired. 

183. To wash the ears carefully. 

184. To refrain from putting anything into the ears. 

185. To refrain from shouting into or pulling other people’s 
ears. 

186. To avoid blowing the nose forcibly, in order to prevent 
possible injury to the ears. 

187. To secure medical advice when there is trouble with the 
ears. 

188. To protect the ears when swimming. 

189. To develop practices of safety. 


278 


PHYSIOLOGY AND HEALTH 
WEIGHT—HEIGHT—AGE TABLE FOR GIRLS 


Height 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

Inches 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

Yrs. 

38 

33 

33 













39 

34 

34 













40 

36 

36 

36 












41 

37 

37 

37 












42 

39 

39 

39 












43 

41 

41 

41 

41 











44 

42 

42 

42 

42 











45 

45 

45 

45 

45 

45 










46 

47 

47 

47 

48 

48 










47 

49 

50 

50 

50 

50 

50 









48 


52 

52 

52 

52 

53 

53 








49 


54 

54 

55 

55 

56 

56 








50 


56 

56 

57 

58 

59 

61 

62 







51 



59 

60 

61 

61 

63 

65 







52 



63 

64 

64 

64 

65 

67 







53 



66 

67 

67 

68 

68 

69 

71 






54 




69 

70 

70 

71 

71 

73 






55 




72 

74 

74 

74 

75 

77 

78 





56 





76 

78 

78 

79 

81 

83 





57 





80 

82 

82 

82 

84 

88 

92 




58 






84 

86 

86 

88 

93 

96 

101 



59 






87, 

90 

90 

92 

96 

100 

103 

104 


60 






91 

95 

95 

97 

101 

105 

108 

109 

Ill 

61 







99 

100 

101 

105 

108 

112 

113 

116 

62 







104 

105 

106 

109 

113 

115 

117 

118 

63 








110 

110 

112 

116 

117 

119 

120 

64 








114 

115 

117 

119 

120 

122 

123 

65 








118 

120 

121 

122 

123 

125 

126 

66 









124 

124 

125 

128 

129 

130 

67 









128 

130 

131 

133 

133 

135 

68 









131 

133 

135 

136 

138 

138 

69 










135 

137 

138 

140 

142 

70 










136 

138 

140 

142 

144 

71 










138 

140 

142 

144 

145 


Prepared by Bird T. Baldwin, Ph.D., and Thomas D. Wood » M*D. 


About what a G I R L should gain each month. 

Age Age 

5 yrs. to 8 yrs. 6 oz. 14 yrs to 16 yrs...8 oz. 

8 “ “ 11 “. 8 “ 16 “ “ 18 “.4 “ 

11 “ “ 14 “. 12 “ ' 

Courtesy of the American Child Health Association 





























































00 cn 


APPENDIX 

WEIGHT—HEIGHT—AGE TABLE FOR BOYS 


279 



Prepared by Bird T. Baldwin, Ph.D., and Thomas D. Wood, M.D. 

About what a B O Y should gain each month. 


Age Age 

yrs. to 8 yrs.6 oz. 12 yrs. to 16 yrs, 

“ “ 12 “.8 “ 16 “ “ 18 “ 


Courtesy of the American Child Health Association 


16 oz 
8 “ 





















































INDEX 


Abscess, 192 
Absorption, 21, 151 
Adrenal body, 223 
Adrenalin, 224 
Air, quality of, 131 
Air sacs, 127 

Alcohol, 13 , 199 , 200, 201, 202, 203 , 
204 , 205 , 206 , 207 
and infectious disease, 205 
and the death rate, 206 
effect on circulatory system, 204 
effect upon nervous system, 201 
Amoeba, 12 
Appetite, 164 
Arteries, 36 , 94 
structure of, 112 
Arteriosclerosis, 112 
Auricle, 105 

Autonomic nervous system, 61 

Bacteria, 13 
Balance, sense of, 77 
Bathing, 236 
Beriberi, 163 
Biceps, 30 
Bile, 150 

Blood, clotting of, 98 
nature of, 98 
plasma of, 102 
Blood corpuscles, 102 
Body temperature, 228 
Bone, 19 
Brain, 54 
areas of, 56 , 58 
diagrams of, 53 , 54 
Brain stem, 59 
Breathing, 126 , 130 
and exercise, 249 
at high altitudes, 134 
control of, 132 
pure oxygen, 135 
Bronchial tubes, 126 
Byrd, R. E., 4 

Caloric requirements, 177 
Calories, 175 
Calorimeter, 178 
Capillaries, 97 


Carbohydrates, 141 
Carbon dioxide, 36 , 175 
Carbon monoxide poisoning, 133 
Caries, 192 
Cartilage, 19 
Cell, diagram of, 15 
structure of, 15 
Cell division, 16 
Cells, 10 
work of, 22 
Cerebellum, 59 
Cerebrum, 55 
Circulation, 94 , 116 
control of, 117 , 118 
portal, 113 
Clothing, 234 
Cod-liver oil, 171 
Coffee, 215 
Color-blindness, 73 
Color vision, 73 
Concentration, 81 
Congestion, 120 
Conjunctivitis, 68 
Conjunctiva, 68 
Connective tissue, 18 
Constipation, 153 
Coordination, 246 
Cotton clothing, 234 
Cretin, 221 

Deficiency diseases, 169 
Dentine, 188 
structure of, 194 
Diabetes, 160 
Diaphragm, 146 
and posture, 256 
diagram of, 224 
Digestion, 144 
and mental states, 168 
Duct, 22 
Dwarf, 222 

Ear, 74 

diagram of, 75 
internal, 76 
middle, 76 
Enamel, 189 
Epithelial tissues, 20 




INDEX 


281 


Esophagus, 146 
Eustachian tube, 75 
Evaporation, 231 
Exercise, 243 
and breathing, 249 
and nutrition, 250 
and the heart, 247 
and the skin, 251 
forms of, 251 
Eye, 67 
Eyeball, 68 

Far-sight, 72 
Fasting, 162 
Fat, 19 
Fatigue, 37 
Fats, 142 
Feet, 257 
Food, 140 
kinds of, 141 
protective, 169 
Food quantities, 174 
Fruit, 167 

Fuel, burning of, 158 
stored, 156 
Fuel value, 175 
Fungus, 2 

Gall bladder, 151 
Gastric juice, 147 
Giant, 222 
Gland, 21 
Glycogen, 157 
Goiter, 221 
Graham flour, 172 
Gram, 174 
Gray matter, 55 

Habit, 50, 81 
defined, 51 

Hearing, defects of, 76 
Heart, 94, 105 
and exercise, 247 
muscle, 106 

Heat, control of in body, 233 
production and loss of, 228 
Hemoglobin, 100 

Impulses, 56 
Inflammation, 121 
Instinct, 3 
Insulin, 161 
Internal ear, 76 


Internal secretions, 161, 217 
Involuntary muscle cells, 149 
Iodine, 163 
Iron, 163 

Kidneys, 159 

Large intestine, 153 
Lens, 70 
Lids, 68 
Lime, 163 
Lordosis, 253 
Lungs, 126 
Lymph, 122 
Lymphatics, 122 

Meat, 166 
Medicines, 216 
Memory, 52 

Mental states and digestion, 168 
Middle ear, 76 
Mind, control of, 89 
health of, 86 
Morphine, 217 
Muscle, 26, 40 
cardiac, 40 
involuntary, 40 
nature of, 31 
voluntary, 33, 40 
work of, 35 
Muscle fibers, 17, 32 
Muscle tone, 254 

Near-sight, 71 
Nerve fibers, 33 
Nerves, 33 
cranial, 47 
optic, 57 
spinal, 46 

Nervous system, 43 
diagram of, 45 
health of, 80 
structure of, 80 
Neurasthenia, 86 
Nose bleed, 98 
Nucleus, 16 

Nutrition and exercise, 250 

Opposing muscles, 30 
Optic nerves, 57 
Orbit, 68 
Oxygen, 36 



INDEX 


282 

Pancreas, ISO, 220 
Pepsin, 148 
Peristalsis, ISO 
Personality, 88 
Pink eye, 68 
Pituitary body, 223 
Pore, 231 

Portal system, 113 
Posture, 253 
sitting, 256 
Protective foods, 169 
Proteins, 142 
Protoplasm, 10 
Pulp cavity, 188 
Pulse, 111 
Pupil, 70 
Pyorrhea, 196 

Red blood corpuscles, 99 
Reflex action, 47 
Reflex, defined, 51 
Rickets, 170 
Roughage, 167 


Scurvy, 170 
Sea food, 167 
Secretions, 21, 46 
internal, 161, 219 
Self-control, 89 
Sensation, 63 
Sense organs, 63 
Sensory fibers, 46 
Shoes, 259 
Skeleton, 27 
Skin, 14 

and exercise, 251 
Sleep, 59 

Small intestine, 146 
work of, 150 
Smell, 66 
Sound, 76 

Spinal cord, 33, 44, 46 
cross-section of, 47 
Spinal nerves, 46 
Spleen, 226 
Starches, 141 
Stereoscopic vision, 73 


Stomach, 147 
work of, 147 
Sugar in the diet, 164 
Sugar, use of, 160 
Sugars, 141 
Suppuration, 121 

Taste, 65, 66 
Tea, 215 
Teeth, 182 

cleanliness of, 196 
formation of, 183 
irregular, 190 
physiology of, 191 
structure of, 188 
Temperature, 103, 228 
Tendons, 18, 30 
Thyroid, 220 
Tissues, 17 

Tobacco, 208, 209, 210, 211, 212, 213, 
214, 215 

and scholarship, 215 
effect upon health, 210 
extent of habit, 207 
Tooth brushing, 197 
Tooth powders, 197 
Trachea, 126 
Triceps, 32 
Tympanum, 74 

Vaso-motor system, 238 
Vegetables in the diet, 167 
Veins, 36 
pulmonary, 95 
structure of, 111 
systemic, 95 
Ventricle, 105 
Villus, 151 
Vision, 70 

Vitamins, 163, 169, 170, 171 
Voice, 137 

Waste products, 175 
Water, 141, 175 
Weight, gaining and losing, 161 
White blood corpuscles, 102 
Woolen clothing, 234 

Yeasts, 13 













































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